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Office: BOU

FXUS65 KBOU 231655

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1055 AM MDT Wed May 23 2018

Issued at 1055 AM MDT Wed May 23 2018

Satellite and radar show showers popping up over the mountain
ridges and tracking northeastward. There appears to be no mid-
level inversion, or capping, which is allowing the showers to
generate fairly early. The shower development seems to be aided by
the right entrance region of an upper jet that is moving over
northwest Colorado. These showers should continue developing
through the afternoon hours. HRRR model runs are showing a batch
of showers moving on to the plains by midday which move across
Larimer, Weld, Morgan and Logan Counties. These may produce hail
up to a half or three- quarters of an inch along with brief heavy
rain. Storm motions should be 15 to 25 mph and to the northeast.
No changes to the forecast are necessary other than moving back
the start time for the showers over mountains.


.SHORT TERM...(Today and tonight)
Issued at 249 AM MDT Wed May 23 2018

Today will be characterized with drier conditions over the
mountains and adjacent plains, while isolated thunderstorms are
forecast over the far eastern plains and will result in a
marginal threat of severe storms.

The Great Basin upper low will continue to lift north and
eastward resulting in a drier southwest flow aloft over central
Colorado and a more subsident airmass. QG fields showing this
subsidence especially over northern mountain sections and more
neutral forcing over the eastern plains. Main change in the
forecast was to reduce storm chances over the mountains and keep
a remaining small threat over the far plains.

Over the eastern plains, surface trof of low pressure will
develop with increasing southwest winds surging northward from the
Palmer Divide. This will set up a convergence boundary with drier
air to the south and the remaining moist air north of the
boundary. Best chance for storms will be north and east of the
boundary, mainly from Limon to Fort Morgan and points north and
east. surface based CAPES progged upwards of 2000j/kg as surface
dewpoints remain in the lower 50s while mid level flow in the
35-45kt range. over the far northeast plains. SPC has much of the
far northeast in a marginal risk for severe storms and this looks
reasonable. Main threat would be large hail and damaging winds.
Mountains and adjacent plains could see isolated showers/storms,
but mainly high based with gusty winds and not much rain.
Temperatures today will be slightly warmer with good mixing below
500mb while 700mb temperatures climb to +12c. Much of the
convection expected to diminish by late evening with clearing

Elevated fire weather concerns over the Palmer Divide with gusty
southwest winds but rh levels not quite low enough to result in
red flag hilites.

.LONG TERM...(Thursday through Tuesday)
Issued at 249 AM MDT Wed May 23 2018

As the closed low exits to the NE Thursday with upper level ridging
increasing over the four corners region. This will help to decrease
convective activity and increase temperatures into the upper 80s to
possibly low 90s by Saturday. Even though atmospheric parameters
during this time is not highly conducive to convective
development, an isolated storm that moves off the higher terrain
and onto the plains cannot be ruled out.

By Sunday, the closed low that was over the Pacific will have moved
onshore over the West coast and into the Great Basin. This will
increase SSW flow with an embedded shortwave moving NNE into the
state Sunday night into Monday morning. Models show the set-up of a
lee side low pulling in strong SE winds over the eastern border
counties and cooler NW with the surface feature. This could help to
determine just how much LL moisture gets pulled into the plains for
convective development. Looking at possible severe storms Monday
afternoon or Tuesday depending on when the ingredients can come
together the best. However, storms will be possible both days.
Temperatures will cool slightly from Saturday with highs in the
low to mid 80s Monday and upper 70s Tuesday.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1055 AM MDT Wed May 23 2018

A few thunderstorms are expected to move out of the foothills and
over the Denver area early in the afternoon. HRRR indicates that
storms should be out of the Denver area by 2 PM or 3 PM. The rest
of the afternoon should see northeast, outflow winds from the
departed showers. Typical drainage winds are expected overnight.




SHORT TERM...Entrekin

Office: PUB FXUS65 KPUB 231738 AFDPUB Area Forecast Discussion National Weather Service Pueblo CO 1138 AM MDT Wed May 23 2018 .SHORT TERM...(Today and tonight) Issued at 444 AM MDT Wed May 23 2018 ...Isolated Storms and High Fire Danger... Dry, southwest flow will bring Red Flag conditions to the San Luis Valley today. Winds gusting above 25 mph, relative humidity below 15 percent and dry fuels will provide conditions favorable for the rapid ignition, growth and spread of fires. Outdoor burning or any other activities that could accidentally start a wildfire should be postponed. Another round of afternoon and evening thunderstorms is expected across southern Colorado today. The best chance for storms today will be across the plains and primarily along and east of a line from Trinidad through La Junta. A marginal severe threat exists along and east of this line today. This area will likely see pre- storm CAPEs of 1500-2000 J/kg and LIs of -4 to -6 before storm initiation around 1 pm. This should be adequate for a few pulse severe storms capable of 1" diameter hail and 60 mph winds along with locally heavy rain and lightning. Shear values don't look all that great, however. Model projections only have 0-6km bulk values at 25-35 kts across the plains. 500 mb wind speeds are progged at SW 30-35 kts but surface winds are only progged at S-SW 15-20 kts. If surface winds end up being more from the SE, we could certainly end up with better shear and a better potential for rotating storms. Will have to monitor that through the day. But for now, it mainly looks like a pulse severe wind/hail threat for the plains today. Convection looks pretty minimal over the mountains and west today as dry southwest flow spreads over the region. It'll be a warm one everywhere with afternoon highs 5-10 degrees above average at most locations. .LONG TERM...(Thursday through Tuesday) Issued at 444 AM MDT Wed May 23 2018 Synopsis: The upper level low that has been affecting the region will propagate to the northeast of Colorado at the beginning of the forecast period. Thursday, a ridge will build over southern Colorado, which will bring exceptionally hot high temperatures to the region. The ridge of high pressure is expected to affect southern Colorado through the Saturday evening into Sunday morning, but will be replaced by another upper low on Sunday. At this point in time, the track of the low will be too far north for severe weather to be an issue, but weak daytime thunderstorms over the mountains, with a few storms making it over the plains, is expected. Thursday: Overnight showers and thunderstorms should dissipate in the early morning hours. During the day, a ridge of high pressure develops over the region with the 586 dam isopleth pushing further north as the day progresses. The air mass associated with ridge will be a particularly dry air mass, with minimum RH values ranging 10 to 15 percent over the SLV and adjacent plains and 15-20 percent across the eastern plains. The low RH values mean that fire conditions are a concern, but will not be considered critical since the surface winds will be too weak. The thunderstorm threat will remain over the far eastern plains, but will be dependent on where the dry line sets up. Variants of the NAM indicate that the dryline will set up over the eastern plains, whereas the GFS puts the dryline east of the region, so there is still plenty of uncertainty in the thunderstorm forecast. The Euro, on the other hand, seems to be a steady compromise of the NAM and the GFS, which puts the dryline near the border of Colorado and Kansas. Either way, the main issue with thunderstorm development Thursday afternoon will be the lifting mechanism, hence why model guidance is having difficulty picking up on any thunderstorm initiation. High temperatures across the plains will surpass the 90s in some locations, the SLV and lower Upper Arkansas River Valley will span the mid to upper 70s, and Lake County will experience the mid 60s. Friday and Saturday: The ridge will continue to affect southern Colorado on Friday and Saturday. The most concerning weather element will be high temperatures. On Friday, high temperatures will be in the low 90s across the plains, low 80s over the SLV and lower upper Arkansas River Valley, and the low 70s over Lake County. Saturday will be the warmest day of the week, with the ridge axis oriented over southern Colorado. Expect temps near 100F over the plains, lower 80s over teh SLV and lower Upper Arkansas River Valley, and lower 70s in Lake County. The thunderstorm threat will be minimal across the region, with the exception of an isolated storm over the mountains. Since the air mass will be so dry there are fire weather concerns for Friday and Saturday. Both Friday and Saturday will likely not meet Red Flag Warning criteria, but the arid air will still cause rapid fire starts. The limiting factor on Friday is the weak surface winds. Saturday, however, will likely hit critical fire weather conditions, but will miss Red Flag Warning conditions due to the temporal constraints not being met. Sunday through Tuesday: An upper level low returns to the intermountain west, currently tracking to travel over Nevada, Utah, then northeasterly over Wyoming. The previously mentioned track isn't conducive for particularly strong thunderstorm, but daily thunderstorms are expected to form over the mountains, with an isolated storm that will travel over the plains. Starting Sunday, the high temperatures will begin declining, but the temperatures will remain well above normal for this time of year. Emphasizing on Sunday now... Critical fire conditions are in the forecast, a may warrant a Fire Weather Watch as the event approaches. Currently, there are minimum RH values in the single digits with sustained wind speeds greater than 20 kts in certain locations. && .AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon) Issued at 1135 AM MDT Wed May 23 2018 VFR conditions expected at the TAF sites over the next 24 hours. Winds will increase from the south to southwest with gusts up to 30 kts possible during the afternoon. Winds will decrease this evening and become light overnight. Isolated thunderstorms will be possible this afternoon, mainly east of a line from KTAD to KLHX. These could become briefly strong producing hail, erratic gusty winds up to 45 kts and MVFR cigs/vis. Most should diminish or move out of southeast CO after 02-03z. -KT && .PUB WATCHES/WARNINGS/ADVISORIES... Red Flag Warning until 8 PM MDT this evening for COZ224. && $$ SHORT TERM...LW LONG TERM...SKELLY AVIATION...KT
Office: GJT FXUS65 KGJT 231641 AFDGJT Area Forecast Discussion National Weather Service Grand Junction CO 1041 AM MDT Wed May 23 2018 .SHORT TERM...(Today through Thursday) Issued at 225 AM MDT Wed May 23 2018 Much drier air is entering the region from the southwest, evident on the low and mid level water vapor channel, as the upper low responsible for the active stormy weather the past few days lifts to the north and into the northern Rockies. Meanwhile, the Front Range from eastern New Mexico to eastern Colorado is dealing with an active stormy night/early morning as convection refuses to go to sleep for the night. Enough moisture and instability will remain up north to trigger afternoon thunderstorm development today. Thinking the coverage will be a little more robust than the models are depicting with areas along the bookcliffs north of I-70 to the Wyoming border being the focus for convective activity. Models also tend to be too quick to dry things out as these upper lows move out of the region. A trailing shortwave disturbance will also move through northeast Utah and northwest Colorado, with a 80 kt upper level jet, which will act as a trigger for convective activity. Expecting higher terrain to be favored although a few storms could drift across the northwest Colorado valleys as the shortwave moves through. Anticipate gusty outflow winds to be the main concerns with storms as the low levels still remain dry, with little in the way of wetting rains. Mostly sunny skies will be the rule south of I-70 with some convective buildups possible over the higher terrain; better chances exists up north. Afternoon temperatures will climb to a few degrees above normal with a noticably warmer day than yesterday due to the lack of overcast skies and less shower activity. The ridge of high pressure continues to build across the Front Range and central High Plains on Thursday as yet another trough of low pressure makes its appearance on the west coast. This will continue southwest flow across the region with temperatures making a bigger jump well into the 80s for most lower valleys, with highs approaching low 90s for some portions of southeast Utah. Dry conditions look to dominate the western slope with a slight chance of thunderstorms over the northern mountains closer to the Wyoming border (eastern Uintas and Elkheads/northern Park range). .LONG TERM...(Thursday night through Tuesday) Issued at 225 AM MDT Wed May 23 2018 The blocky pattern will remain in place across the Lower 48 through the extended period with the stronger jet stream located well to the north. Ridging will become well established over the Rockies by Thursday night and will really slow the next upstream system which may not bring any precipitation until late in the weekend or not at all depending on which model ultimately verifies. Warm and dry southerly flow will lead to a high probability of well above temperatures Friday into Saturday with only a slightly lower probability going into Sunday for the same reason as above. The storm will move into the Great Basin by early Sunday and then basically stall due to the downstream block, a relatively common theme late this Spring. So as rain falls back to the West, windy conditions will develop over our CWA this weekend and this will exacerbate critical fire weather conditions where fuels have not greened up or retained much moisture. QG structure of the system centered near the UT/NV border remains well out of phase with the GFS taking on a more E-W configuration and the EURO more N-S and compact. Still little confidence going past Saturday but the general theme would be slight cooling by Sunday into early next week as the thermal ridge is pushed more into the High Plains. The probability of precipitation during this time is likely higher near the Wyoming border and close to zero near the New Mexico border. Don't shoot the messenger. && .AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon) Issued at 1041 AM MDT Wed May 23 2018 Isolated to scattered showers and thunderstorms are expected to develop over the northern mountains early this afternoon then, once formed, will continue through 02Z this evening. This activity poses little threat to TAF sites, though KVEL and KHDN may experience brief and unpredictable outflow winds from storms over higher terrain in the vicinity. Otherwise, VFR conditions will continue through the next 24 hours with CIGS above ILS breakpoints at all TAF sites. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...None. UT...None. && $$ SHORT TERM...MDA LONG TERM...15 AVIATION...NL