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Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
1149 PM CDT Tuesday Mar 31 2015

Update...
issued at 1058 PM CDT Tuesday Mar 31 2015

Temperatures were dropping rapidly this evening due to the very
dry air...light winds and clear skies. Of the short term
models...only the latest hi res rap was coming close to capturing
the rate of fall...which is several degrees ahead of the other
short term models and the forecast.

In-coming high thin clouds in the northwest flow out of the plains and a
weak southeast return flow developing toward morning ahead of the plains
trough should slow the rate of fall toward sunrise. Ahead of
this...will have several more hours of ideal radiational cooling
and have thus updated the forecast to lower mins to the lower 30s
north and northeast...while the SW should still be limited to the
middle 40s. Some valley sites in the north will likely drop below
freezing.

&&

Synopsis...
issued at 346 PM CDT Tuesday Mar 31 2015

Temperatures well above normal and mainly well in the 60s to lower 70s at 3pm
with deep mixing...dry ground and abundant sunshine. The only
exception being portions of far northwest Illinois counties which are seeing
more cumulus where better low level moisture lingering in wake of
lake enhanced boundary limiting temperatures to upper 50s/near 60 few spots.

Passage of surface and upper level ridging supports dry and mainly
clear skies much of next 24 hours.

&&

Short term...(this evening through wednesday)
issued at 346 PM CDT Tuesday Mar 31 2015

Surface ridge axis will pass through the County Warning Area this evening then shift
into Ohio Valley overnight. Skies will be mainly clear with winds
becoming light then shifting to southeast and south overnight.
Coolest low temperatures (mainly 30s) favored northeast half of County Warning Area with
milder lows in the 40s far west and southwest County Warning Area where stronger
southerly winds expected to develop overnight.

Wednesday...main item is fire weather concerns otherwise... windy and
warm with highs in the 70s areawide beneath mainly sunny skies.
The gusty southerly winds 15-30 miles per hour and dry vegetation combined with
lowering relative humidity values will pose very high to extreme fire
danger potential. See fire weather section below.

Long term...(wednesday night through tuesday)
issued at 346 PM CDT Tuesday Mar 31 2015

Forecast focus on thunderstorms Wednesday night then a snow
potential on Friday. Convectively active pattern next week.

Wednesday night...most operational models have slowed the system
just enough to keep the first half of the evening dry. Forecast
soundings show dry low levels. Believe the GFS is a bit too
aggressive with bringing quantitative precipitation forecast eastward. This slower movement also
diminishes the potential for stronger storms and indeed Storm Prediction Center has
shifted the marginal severe farther to the west of the dvn County Warning Area.
Upper level trough will provide large scale ascent and with
increasing moisture showers and thunderstorms will be at least
likely. Rainfall amounts may potentially be up to an inch in our
western County Warning Area...with lesser amounts farther east.

Thursday...showers and thunderstorms will gradually end from northwest to
southeast as a cold front pushes slowly across the County Warning Area. Temperatures will
be cooler with highs in the lower to middle 60s.

Friday...interesting scenario as colder air invades the County Warning Area as a
secondary cold front and upper level trough push into the region.
The European model (ecmwf)/GFS allows for cyclogenesis in the Southern Plains to push
northeast and intensify as it tracks into the Ohio Valley. 850 mb
temperatures lower to -4 to -6c which would suggest rain turning to
snow. However...1000-500 mb thickness values don't cool down to the
traditional 540 thickness for snow until later in the afternoon and
by that time the deeper moisture is starting to shift to our east.
Other factors to consider to downplay any accumulation is this is
occurring during the day and the ground will be warm. For now will
mention rain/snow mix or changing to snow in the afternoon.
Temperatures will also be falling during the day into the 30s.

Sunday through Tuesday...active convective pattern as upper flow
becomes more southwesterly combined with Gulf moisture transport...
along with synoptic boundaries pushing into the Midwest. This
appears to be a period of active thunderstorms along with mild to
warm temperatures.

Haase

&&

Aviation...(for the 06z tafs through 06z Wednesday night)
issued at 1149 PM CDT Tuesday Mar 31 2015

VFR conditions with light winds and clear skies will be the rule
through the rest of tonight through early Wednesday morning.
Light south winds will increase to 15 to 25 kts or stronger by
late morning ahead of a developing cold front in the plains. This
cold front will push through the area late Wednesday
night...accompanied by showers and thunderstorms. At the
earliest...thunderstorms may reach the brl...Cid and dbq terminals
between 03z and 06z...but are more likely to be widespread after
the 06z taf ending period and thus not included in the latest
forecasts. Gusty south winds will likely be sustained at 15 to 20
kts well into the evening hours.

&&

Fire weather...
issued at 346 PM CDT Tuesday Mar 31 2015

Southerly winds will increase on Wednesday into range of 15 to 25 miles per hour
with gusts to near 35 miles per hour at times. This coupled with very dry
vegetation will lead to a very high to extreme risk of fire danger
on Wednesday. There is some potential for red flag warning
criteria being met...especially portions of eastern Iowa where
currently forecasting min relative humidity values near 25 percent
and winds near 25 miles per hour sustained criteria. Given the above have
gone with a Fire Weather Watch for portions of eastern Iowa where
the red flag warning criteria closest to being met and where GFDI
values are in extreme category. The concern is that with dry
ground and slightly backed southeast wind just off surface pulling
in dry air from departing high that the dewpoints forecast in the
upper 30s to lower 40s may be a bit too high. When mixing down
from forecast soundings (875-850 mb) actually yields lower dewpoints in
middle/upper 30s fairly widespread. Thus...could see more of area
closer to red flag warning criteria.

&&

Dvn watches/warnings/advisories...
Iowa...Fire Weather Watch from 10 am CDT Wednesday through Wednesday
evening for Benton-Buchanan-Delaware-Henry Iowa-Iowa-
Jefferson-Johnson-Keokuk-Linn-Van Buren-Washington.

Illinois...none.
MO...none.
&&

$$

Update...sheets
synopsis...05
short term...05
long term...haase
aviation...sheets
fire weather...05

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