Air Resources Laboratory banner image
Air Resources Laboratory web site National Oceanic and Atmospheric Administration (NOAA)

ia discuss

Office: DMX

FXUS63 KDMX 250538

Area Forecast Discussion
National Weather Service Des Moines IA
1138 PM CST Sat Feb 24 2018

.SHORT TERM.../Tonight through Sunday/
Issued at 324 PM CST Sat Feb 24 2018

Bulk of forcing is ongoing this afternoon with strong kinematics and
good isentropic lift.  Mid levels have remained relatively dry
except in far western and northern areas leading to widespread
drizzle across much of central and southern Iowa as temperatures
have climbed above freezing east of a line from Mason City through
Fort Dodge to Atlantic.  Will continue to see saturation deepen
ahead of approaching front with precipitation becoming heavier late
this afternoon into early evening along the front as it progresses
eastward across the forecast area.  Northern Iowa will see strictly
snow which may be heavy at times with convective elements
progressing northward into Minnesota.  Total amounts may not be as
high as previously thought but 2 to 4 seem reasonable.  Farther
south, drizzle and rain are expected to persist ahead of the front
with temperatures remaining above freezing.  However, there will be
some snow coincident or just behind the front as cold air advects
quickly in on the backside of the boundary.  If any convective
elements develop along the front, there may be a brief period of
heavy snow with them as well.  Otherwise, there is also some concern
where the winds are light this evening prior to frontal passage that
fog may quickly thicken.  While this will only be for a short time
prior to the front passing, it may become dense until the heavier
precipitation begins.  Overall snow amounts in central and southern
Iowa will be minimal.  The advisory will be maintained in all areas
but it remains very marginal on the southeast side where snow
amounts will be quite light.  The biggest concern will be the cold
air arriving on the backside of the front with strong west winds
helping water on roads to freeze somewhat quickly.  This may lead to
some icing concerns into the evening.

Otherwise, once the front passes, strong west winds and clearing
skies are forecast overnight as cooler air arrives.  Relatively
strong subsidence is then expected into Sunday with some sunshine as
westerly flow at the surface.

.LONG TERM.../Sunday night through Saturday/
Issued at 324 PM CST Sat Feb 24 2018

Summary...Quiet weather will dominate the next few days, along with
temperatures rising above freezing, even into the 50s across the
south. Wed/Thur could be impactful with guidance beginning to show
some semblance of agreement of a large wrapped up low sliding across
SE Iowa. Implications may range from heavy rainfall to blizzard-like
conditions across Iowa.  Quiet, relatively warm weather returns to
end the week/start next weekend.

Sunday through Wednesday Morning...By Sunday, upper level flow will
being to become predominantly zonal across CONUS as the upper level
system responsible for the freezing rain/snow Saturday departs into
the Great Lakes and eastern Canada. The zonal upper level flow and
surface return flow will be in place through mid-week, resulting in
temperatures gradually rising over the next few days, topping out
Wednesday in the 40s/50s.  A weak backdoor cold front will likely
keep northern Iowa from tapping into the 40s Tue/Wed, as high
pressure slowly slides across the Dakotas.

Wednesday Afternoon through Thursday...Easily the greatest potential
for impactful weather over the next 7 days. GFS has shown relative
consistency in developing a cutoff upper low and surface reflection
as an upper level trough ejects out of the SW US.  Euro has
predominantly held off on developing anything of that strength,
keeping it as an open wave, however that changed with the 12z run.
Euro now in fair agreement with the GFS, depicting a tightly wound
surface low approaching 986 mb. Should this come to fruition,
blizzard-like to blizzard conditions appear likely somewhere over
N/NW areas. Elsewhere further S, heavy rain to thunderstorms.  Given
Euro flip just in the last run, confidence too low to make any large
changes to the forecast.  Should consistency remain over the next
couple runs, a ramp up in messaging will likely be necessary, among
other things such as increasing winds, etc... A big hindrance to
precip type at the moment is high variability in the ensembles,
approaching 5 standard deviations in some cases, only adds to low
confidence in overall ability to make gainful changes to the
forecast at this time. Once again, easily the time frame to pay
attention to.

Friday through Saturday...Quiet weather returns with ridging
depicted across also synoptic guidance. Temperatures would appear
set to rise back into the 40s/low 50s by Saturday.


.AVIATION.../For the 06Z TAFS through 06Z Sunday night/
Issued at 1137 PM CST Sat Feb 24 2018

Area of MVFR cigs still passing across much of Iowa though will
continue move east overnight with conditions becoming VFR and will
then last through Sunday. Breezy west winds overnight will
diminish a bit on Sunday.




LONG TERM...Curtis

Office: DVN FXUS63 KDVN 250518 AFDDVN Area Forecast Discussion National Weather Service Quad Cities IA IL 1118 PM CST Sat Feb 24 2018 ...06z AVIATION UPDATE... .SYNOPSIS... Issued at 310 PM CST Sat Feb 24 2018 An overcast sky and cold east breeze continued during the early afternoon, with areas of light rain, drizzle and light fog. Temperatures were mainly in the 35 to 40 degree range. A large area of showers and embedded thunderstorms approached the area from the south, but are only expected to brush far northeast Missouri and west central Illinois through the late afternoon. && .SHORT TERM...(Tonight) ISSUED AT 310 PM CST Sat Feb 24 2018 The main forecast issues in the short term period are precipitation type and amounts tonight, and strong westerly winds. In the near term, high res models have a good handle on the rain shield to the south, and barely clip the southern counties through late afternoon. The main period of precipitation will be from 5 pm to 11 pm as rain spreads across the entire forecast area. Rainfall amounts are not expected to be high enough to cause further river flooding, but there may be some nuisance ponding. A few thunderstorms may develop during the early evening, mainly along and east of the Mississippi River. The favorable severe weather parameters should remain well to the southeast, although an isolated storm may generate some small hail. Cooling aloft should be sufficient for a quick change over to all snow in the far northwest, with any wet accumulations likely limited to less than an inch. Precipitation should be all rain elsewhere across the forecast area. After midnight, a strong westerly wind will increase, with gusts of 35 to 40 mph. Due to the wet nature of any snow, blowing snow should not be an issue, although there may be some shallow drifting in the far northwest counties. Am not expecting advisory criteria winds at this time. .LONG TERM...(Sunday through Saturday) ISSUED AT 310 PM CST Sat Feb 24 2018 Sunday...Post frontal, drying day with lingering brisk west winds of 15 to 25 MPH decreasing late in the day. Mixing wind profiles, combined with some late Feb insolation to help temps make it up well into the 40s acrs most of the area. Overnight lows in the 20s, and will have to watch developing light south to southwest llvl flow for non-diurnal trends into Monday morning on backside of departing sfc ridge. Monday and Tuesday...The latest suite of 12z run medium range models generally dig a closed upper low into a L/W Trof acrs the desert SW and far northern Baja this period, while resultant broad southwesterlies take shape from the deep southwestern plains to the southern GRT LKS. Increasing southerly LLVL flow to make for two seasonably mild days this stretch, with some upper 50s to low 60s likely by Tuesday. A sfc boundary sagging down acrs the region and becoming increasingly aligned and stalled under this flow, may act as a moisture convergence agent by Tue night. Light precip may break out in the vicinity of this feature, and depending on where it lays out, occur in the local area. the 12z GFS and NAM suggest light rain along this feature north of I80, with some possible precip type issues popping up north of the boundary late that night if sfc/BL temps can cool enough. Other precip fields may be advecting into the southern CWA at that time as well but would remain all rain down there. The 12z ECMWF is mainly dry through 12z Wed with the front hanging up further to the northwest. May be some localized fog issues as well around the front late Tue night. Wednesday through next Saturday...Main feature of consequence this mid to late week period, is that several medium range models roll out east-northeastward the western upper trof, resulting in a "bowling ball" of a llvl cyclone rolling east somewhere acrs the MS RVR Valley. Much will depend on eventual phasing and handling of this wave, but several models such as the 12z GFS and ECMWF are unusually/unseasonably wet with this system. Potentially heavy rain in or near the local fcst area(if the latest models are near to being correct...a big "if") mainly from late Wednesday through Thursday. On the western flank of this rather slow roller, strong sfc winds and dynamical cooling may make for some dicey winter-type conditions with wet snow accums in the west and northwestern fcst anywhere form late Wed night into Thu, again if current model timing and top-down cooling parameters unfold. The models will continue to vary and be inconsistent with their phasing of this system, and will have to look a upper jet trends around this potentail low pressure system as well over the next several days. Can the sfc low really deepen below 990 MB like the latest models indicate as it passes eastward acrs the area? Temp trends on either side of the system along with the potential QPF, still vary much up in the air and will make just general trends for now of the latest solution indications. Dry ridging both at the sfc and aloft should follow into the start of next weekend in the wake of whatever storm system can(or cannot) materialize during the midweek. ..12.. && .AVIATION...(For the 06Z TAFS through 06Z Sunday Night) ISSUED AT 1114 PM CST Sat Feb 24 2018 MVFR ceilings will give way to clearing skies and VFR conditions prior to daybreak, as drier air overspreads the region. Winds will be gusty from the west/southwest at around 30-35 kts at times as well. Sunday will bring a continuation of VFR conditions with gusty southwest winds 15-25 kts diminishing at or below 10 kts by evening. && .HYDROLOGY... Issued at 1134 AM CST Sat Feb 24 2018 Rock River Major flooding continues to affect Joslin and Moline along the Rock River. Joslin has reached crest and has begun slowly falling over the past few hours, with the current forecast taking it below major flood stage by late Sunday afternoon. However, changes in river levels are possible until ice completely breaks up. Pecatonica River A crest into major flooding is expected at Freeport early morning Monday. Also, renewed rises on Yellow Creek are possible, so people affected by the creek should remain alert. Rainfall amounts up to 0.3 inches are expected tonight. This additional rain is not expected to have a significant impact on area rivers. && .DVN WATCHES/WARNINGS/ADVISORIES... IA...NONE. IL...NONE. MO...NONE. && $$ SYNOPSIS...RP Kinney SHORT TERM...RP Kinney LONG TERM...12 AVIATION...McClure HYDROLOGY...Speck