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Area forecast discussion
National Weather Service Quad Cities Iowa Illinois
331 am CST Sat Nov 25 2017

issued at 302 am CST Sat Nov 25 2017

A cold front, which swept across the area last evening, is well
off to our east and extends roughly near a line from Lansing
Michigan to St Louis MO at 07z. This means our record warmth is now
being replaced by much cooler conditions, relatively speaking as
still seasonably mild with temperatures hovering at or above normal
highs for the date early this am. Further west, high pressure
extends from the northern rockies into the Central Plains. This
high will build into the area tonight bringing seasonably cold and
tranquil conditions.


Short term...(today and tonight)
issued at 302 am CST Sat Nov 25 2017

Northwest winds gusty at times 15-25 mph for much of today will
continue to advect in cooler air. The strongest cold air advection and coolest
temperatures will be found from northeast Iowa into far northern IL,
where highs likely to be in the mid to upper 40s while 50s will be
common elsewhere beneath plentiful sunshine. These temps are still
seasonably mild /above normal/, but likely not feeling quite as such
after coming off record shattering warmth.

High pressure will build into the area tonight providing tranquil
and cold conditions. Skies likely to be mostly clear with just
some high thin cirrus, which may increase some overnight as a low
amplitude wave dives through the Missouri River valley but shouldn't
have much if any impact on lows. Strong radiational cooling setup
with shallow, steep low level inversion supports siding near the
colder side of guidance for lows in many areas. Likely to see lows
in the upper 20s and lower 30s, with some mid or even lower 20s
possible in drainage and other low lying areas based on 850 mb temp
rule and steep inversion. Latest NAM is trending a bit faster in
moving out the high, toward 09z through 12z, and developing light
southerly winds which could lead to a small rebound on temps or
slightly warmer lows late tonight, especially north/west sections of

Long term...(sunday through friday)
issued at 302 am CST Sat Nov 25 2017

Sunday and Monday...even after a cold start to the day, increasing
southerly return flow as the day progresses(probably more than the
models suggest) and ongoing ambient dry conditions to help Sunday
highs reach well up in the 50s acrs much of the County Warning Area. Ongoing
southerly winds and cirrus spilling down off Western Plains ridge
and south of upper jet axis to make for a milder night Sunday night
with lows held up at least in the 30s. Upstream thermal ridge to
then adjust eastward acrs the region on Monday, with thermal
profiles projected to not be all that dissimilar to what occurred
earlier this black Friday. Mixing depth with enhanced inversion
aloft, to be critical to high temp potential and how brisk the
southerly sfc winds get, but a good chance for temps to be well up
in the 60s with even a 70 possible again...near record highs for Nov
27th. If adequate mixing depth attained to help transport higher
winds to the sfc, as well as produce lowering sfc relative humidity bombs/dpt dry-
Downs, another enhanced fire threat to Grasslands looks to be on tap
for Monday.

Tuesday and Wednesday...latest suite of 00z run medium range models
still dig an upper level trof into the northern Great Lakes by late
Tuesday, shunting an associated frontal system through the area.
This feature to be pushing into a dry airmass, and the models vary
again from a dry frontal passage ECMWF, to the GFS with bands of light rain.
Adequate saturation depth could be a problem, and if it's just a
shallow layer along the front could just see drizzle or spotty
sprinkles along and Post-frontally. For now will adjust slight chc
pops for light rain mainly Tue afternoon along and east of the river
oriented from NE-to-SW behind the front at that point. Wednesday a
low confidence day with the models having trouble staying consistent
in handling southwestern Continental U.S. And Southern Plains developing cut-
off upper low as it gets dragged east. But the latest general trend
is an unphased further south much so that the County Warning Area may
remain largely dry Wed into Wed evening. The 00z GFS does develop an
elevated frontogenetical forced band of light precip acrs the
central and southern County Warning Area by late Wed afternoon and evening, which
eventually may get aided by northern plains digging upper trof Wed
night. If precip does break out this period, thermal profiles are
that most of it should fall as rain.

Thursday and next Friday...phasing and saturation issues remain, but
the latest medium range model trends/ensembles suggest that late Wed
night into Thu may be the main precip window potentail as upstream
upper trof axis shears acrs the mid and upper MS River Valley regions.
Low to mid level thermal profiles at this time still suggest mainly
a cold rain to fall if this scenario pans out. Even if the rain
exits off to the east by Thu afternoon like the current runs of the
GFS and Euro suggest, cool advection to make for the coolest day of
the period with highs held well down in the 40s. Then drying and
moderating temps into the end of the week with arrival of upstream
ridge complex from the Western Plains. ..12..


Aviation...(for the 06z tafs through 06z Saturday night)
issued at 1118 PM CST Fri Nov 24 2017

Strong and gusty northwest winds that overspread the region behind
a cold front Friday evening will diminish and become sustained
around 10 to 15 kts overnight into Saturday afternoon. Winds will
then become light westerly by Saturday night as high pressure
moves into the area. Conditions will remain VFR throughout under
mostly clear skies.


Dvn watches/warnings/advisories...


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