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Office: DVN

FXUS63 KDVN 172313

Area Forecast Discussion
National Weather Service Quad Cities IA IL
613 PM CDT Sat Mar 17 2018


Issued at 310 PM CDT Sat Mar 17 2018

At 2 PM CDT, skies are clearing with weak surface high pressure moving
in with fair skies and cool mid march temperatures in the 40s north
and upper 30s south. The area to remain in between systems with near
to below normal temperatures and dry into late in the upcoming week.


.SHORT TERM...(This Evening through Sunday)
ISSUED AT 310 PM CDT Sat Mar 17 2018

Short term forecast confidence assessment...fair or average with main
concerns cold air drainage tonight with possible areas of fog. If winds
becoming light after midnight some mins may be 3 degrees or more too

Tonight...mostly fair to fair with light winds by late evening. Patchy
to areas of fog are possible mainly in the southern sections. Area mins
are mostly 25 to around 30 degrees south with risk of some lower mins
possible in the northern 1/2 sections.

Sunday...fair to mostly fair with light winds and highs upper 40s to
the middle 50s or near seasonable for late March.

.LONG TERM...(Sunday Night through Saturday)
ISSUED AT 310 PM CDT Sat Mar 17 2018

Forecast focus on mainly dry conditions for most of next week with a
strong storm system arriving late in the week into next weekend.

Sunday night through Thursday: The pattern will be dominated by high
pressure to our north forcing the storm track south of the dvn cwa.
For the most part this will be a dry and rather cool period with
highs mainly in the 40s to lower 50s and lows in the mid 20s to mid
30s. Did maintain slight pops in our far south for Monday into
Monday evening per coordination with surrounding offices, but the
models have trended farther south and later shifts may be able to
remove the slight pops.1800/1824 09006KT

Thursday night into next weekend: Low confidence this far out in
regards to timing/intensity and type of precipitation and amounts.
Models indicate a decent storm system arriving in the Midwest with a
nice moisture transport northward out of the western Gulf. Looks
cold enough for snow on the leading edge of the strong warm air
advection, then changing to rain and possible thunderstorms,
followed by snow at the back end of the storm system. However, there
are big discrepancies on the timing and thermal profile of the
atmosphere. The ECMWF is stronger with the cyclone and also much
colder behind the system compared to the GFS. Stay tuned!


.AVIATION...(For the 00Z TAFS through 00Z Sunday Evening)
ISSUED AT 612 PM CDT Sat Mar 17 2018

High pressure moving into the region will provide mostly clear
skies and light winds tonight through Sunday. Lingering low level
moisture over southeast Iowa and west central Illinois will create
favorable conditions for fog formation tonight into early Sunday
morning. The new forecasts include a transition to IFR, 2SM to
3SM visibilities, at CID, MLI and BRL. Conditions could
potentially go much lower lower, with some model guidance
suggesting visibilities below one quarter mile toward morning.
Confidence was not high enough to go that low at this time, but
trend trends will be monitored closely for possible updates this





Office: LOT FXUS63 KLOT 172324 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 624 PM CDT Sat Mar 17 2018 .SHORT TERM... 148 PM CDT Through Sunday... Lingering light precipitation will continue to dwindle south of I-80 this afternoon, otherwise clearing skies and diminishing winds will be the trends into tonight. Sunshine and temps in the 50's expected for Sunday, through light winds will allow a lake breeze to develop and drop temps into the lower 40's near the lake in the afternoon. Weakening surface low pressure was over the lower Ohio Valley of western Kentucky early this afternoon, associated with the upper level low which was shearing/dampening eastward across the region. Some patchy lingering light precipitation persisted over the southern half of the forecast area within the shearing deformation axis north of the mid-level vort center, with some reported mixed rain/sleet/snow per mPING, though surface temps in the mid-30's and dew point temps above the freezing mark indicate freezing precip is not a concern. High-res guidance remains consistent in continuing to weaken/dissipate this precip over the next several hours, ending before evening as the mid-level wave continues to drift off to the east-southeast. Farther north, dry northeasterly low-mid level flow has helped to clear clouds across far northern IL, generally along and north of I-88. This clearing will continue to work south through the remainder of the afternoon and early evening hours, leading to mainly clear skies overnight. Strong mid-level height rises develop this evening as the short wave tracks away from the region and upper ridge moves east from the Plains. Subsidence results in surface high pressure drifting across the region into Sunday, allowing our current blustery northeast winds to diminish to light/variable flow tonight and Sunday. May be some patchy shallow fog development across southern parts overnight of the cwa where clouds clear late and dew points remain a bit higher. Sunshine Sunday, combined with light winds, should make for pleasant early-Spring weather. 925 mb temps of +4/+5C should allow for afternoon highs in the low-mid 50's, though the presence of the weak pressure gradient within the surface ridge axis will result in lake breeze development off Lake Michigan by early-mid afternoon, which will cool area near the lake quickly back into the 40's. Overall however, not a bad end to the weekend. Ratzer && .LONG TERM... 300 PM CDT Sunday night through Saturday... For those hoping for a warmer weather after what will be a pleasant Sunday away from the lake, unfortunately the upcoming work week will be a cool one. This will be due to persistent northeastern North America/North Atlantic blocking (-NAO) keeping broad mid-upper troughing locked in over the region and Canadian high pressure anchored to our north. The high pressure will result in prolonged and occasionally gusty northeast surface flow, which will keep lakeshore areas particularly chilly and in the 30s to possibly around 40 much of the time. The blocking pattern does now appear likely to result in surface low track far enough south to keep precipitation from the Monday-Tuesday system mostly south of the CWA, with much better ensemble agreement than yesterday. Can't yet rule out a slight adjustment back north, but if any light precip occurs, it will likely be well south of I-80. As mentioned above, the main sensible weather effect of the described surface pattern Monday-Tuesday will be northeast winds gusting up to 25 to 35 mph, strongest near the lake (particularly on Monday-Monday night). Dry conditions appear likely to persist influenced by surface high pressure Wednesday-Thursday. A strong short-wave will eject out of the next western trough late in the work week, with a robust surface low likely taking shape over the High Plains. The blocky pattern will modulate the track of this surface low as well as gradually weakening it eastward over next weekend. Current consensus of the operational and much of the ensemble members are for the low to be forced over or south of the CWA. There's overall solid agreement in a storm system affecting the region, however as is to be expected 6-7 days out, there's plenty of uncertainty with specifics, including timing. With steady precipitation expected on Saturday, lowered high temperatures to upper 30s-mid 40s, which could certainly be generous considering most raw guidance is cooler than this. In fact, depending on the exact track and strength of this likely storm system, thermal profiles in portions of the CWA could be supportive of wet snow even during the day on Saturday. Stay tuned and expect plenty of changes. Castro && .AVIATION... For the 00Z TAFs... Only weather related item of note aviation-wise next 24-30 hours is lake breeze wind shift expected Sunday afternoon. Winds behind the lake breeze likely to be in the 09-12kt range before diminishing after sunset. - Izzi && .MARINE... 324 PM CDT High pressure will move across the southern part of the lake tonight while low pressure drops southeast across Lake Huron. This low will shift winds across northern and central parts of the lake from westerly overnight to northerly by Sunday morning. The north to northeast winds will increase going into Sunday night as high pressure builds across Ontario and low pressure takes shape across the central Plains. As this low tracks east on Monday, the pressure gradient will increase across the lake, driving northeast winds to 30 kt. The low pressure track is appearing to be far enough south to preclude gales over the southern half of the lake and nearshore waters, but can't rule gales out yet. Winds will gradually ease on Tuesday, but given the prolonged northeast flow, expect hazardous waves for small craft to persist into or possibly through Tuesday evening. A northeast to north flow over the lake is expected to continue much of the rest of the week. The next stronger storm system could track close enough south of the lake to bring 30+ kt winds Friday night into Saturday. Castro/MTF && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO
Office: ILX FXUS63 KILX 180215 AFDILX Area Forecast Discussion National Weather Service Lincoln IL 915 PM CDT Sat Mar 17 2018 .UPDATE... Issued at 900 PM CDT Sat Mar 17 2018 Drier air is beginning to filter in across central and southeast Illinois from the north in the wake of the system that passed through the Midwest earlier today. While the arrival of this drier air and departure of forcing with the system has ended the precipitation risk, tonight's forecast is still a little tricky. Skies across the forecast area have started to clear from the north, and this clearing should continue to expand southward overnight. The ground surface is wet across most of the area due to precipitation that occurred over the past 24 hours. This fact, combined with light winds and clearing skies would seem to be a good setup for fog later tonight. Most of the high resolution guidance suggests light fog development later tonight, with pockets of locally dense fog. Guidance generally suggests the thickest fog will be over southwest portion of the forecast area, which will also be one of the last areas to clear. Would generally expect areas that clear sooner to have thicker fog since they have longer for radiational cooling and associated saturation to occur. Going forecast already had mention of patchy fog and see no reason to deviate from this right now. Plan to update forecast for the latest hourly trends (mainly sky cover). Can't rule out the need for stronger fog mention or possibly an advisory before morning, but confidence is not high enough to adjust at this time. && .SHORT TERM...(This evening through Sunday) ISSUED AT 303 PM CDT Sat Mar 17 2018 Ridging at the surface and aloft over the Plains this afternoon, keeping a northerly component in the winds over the forecast area. Cooler air filtering into the region, but the stubborn stratus associated with the low passing through the Midwest into IN this afternoon is slow to erode. HRRR slowly progresses this shield of clouds to the south tonight, eventually moving to mostly clear for Central IL by morning. Concerned that the dry air is a little further to the north than prev addition to the fact that there is not significant llvl flow to change the airmass quickly. Lighter winds in the overnight combined with llvl moisture still trapped in the low levels may slow the progression of the low clouds to the southwest. There is currently a good 30 mile or so lag of the dry air behind the clearing line to the north/northeast. With that in mind, have put patchy fog in the forecast after midnight for where the clearing is anticipated. Should the delay last longer, there is a potential for some of that fog to become dense...but guidance winds stay up just enough to drop confidence in that for now. Tomorrow, mild temps with highs in the 50s. The swath of low clouds holding just to the southwest with light easterly winds attempting to advect some of that drier air in at the surface. How far south those clouds get will greatly impact temperatures particularly SW of a line from Macomb to Decatur. .LONG TERM...(Sunday night through Saturday) ISSUED AT 303 PM CDT Sat Mar 17 2018 Overnight Sunday into Monday...lows drop only to the low to mid 40s as increasing clouds once again inhibit cooling in the overnight hours. Next system for Monday/Monday night went with a more southerly solution this run, with the GFS and ECMWF keeping the associated precip well south of the NAM solution. Given the erratic nature of the solutions out of the models at this point, keeping the slight chc/chc pops across the northern tier for now. Rain for Monday and Monday night is expected, before briefly changing over to snow on its departure to the east on Tuesday. Models are relatively consistent in suggesting that this wave will shift us back to a busier and more progressive northwesterly flow pattern aloft. Several waves suggested in this pattern, but the GFS is pretty robust with the development of a surface ridge, inhibiting precip development (Wed night in particular). Low confidence dry forecast through the middle of the week once the northwesterly flow kicks in. The next major storm is taking shape going into next weekend, with precip starting on Fri. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) Issued at 653 PM CDT Sat Mar 17 2018 Low-end MVFR CIGS will sink south of central Illinois this evening, providing a return to VFR conditions. However, expect at least MVFR fog to develop across the area later tonight. Once the fog burns off Sunday morning, VFR are expected. Light winds will prevail through the 00Z TAF valid time. && .ILX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...Bak SHORT TERM...HJS LONG TERM...HJS AVIATION...Bak