Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 231800

Area Forecast Discussion
National Weather Service Quad Cities IA IL
100 PM CDT Wed May 23 2018


Issued at 255 AM CDT Wed May 23 2018

High pressure was centered over WI and northern IL early this AM.
Light winds and mainly clear skies has allowed temps in these
areas to drop into the lower to middle 50s, and also resulted in
the formation of some fog. Further west temperatures were being
held up in the 60s due to cloud cover and light east/southeast
winds. Elevated arcing band of storms extends from southwest MN
through north central IA early this morning. Convection was
occurring within zone of strong theta-e advection and 850 mb
convergence/ confluence downwind of mid level instability axis.
Meso-Beta Elements (MBEs) moving southeast at a right angle to
inflow creating a favorable setup for repeated activity and
locally heavy rain. With MBE vectors from northwest, and low level
jet (LLJ) veering but weakening we will have the potential to see
some propagation and/or development of convection into eastern IA
until mid morning before nocturnal LLJ and attendant kinematic
processes wane.


.SHORT TERM...(Today and Tonight)
ISSUED AT 255 AM CDT Wed May 23 2018

Will have mention of fog along and especially east of the Mississippi
River through daybreak. Fog could be patchy dense in portions of
northern IL. Otherwise, watching the convection over north central
IA. Will have low to moderate PoPs until mid morning for portions
of eastern IA (mainly along/n of I-80) to account for possibility
of scattered elevated showers and even a few storms drifting and/or
developing into some areas west of the Mississippi River before
LLJ wanes. Lightning and locally heavy downpours are the main threats
from any storms. For the afternoon expecting partly to mostly sunny
skies. Humid conditions are on tap west of the Mississippi River
within low level moist axis characterized by dew points in the 60s.
Slightly drier air with dew points in the 50s expected into northern IL
being in close proximity to departing high. Highs should top out in the
upper 70s to middle 80s. Can`t completely rule out a shower or weak
storm late this afternoon across the far south with convective
temps breached, but lack of any other apparent trigger lends support
for too low of coverage for mention... should it even occur.

Tonight, mainly clear to partly cloudy. Elevated weak theta-e advection
may lend to some accas and low potential of a shower west of the
Mississippi River, but again in absence of other trigger any coverage
would appear too isolated for mention. Lows coolest east (mid/upper 50s)
and warmest south/west (mid 60s).

.LONG TERM...(Thursday through Tuesday)
ISSUED AT 912 AM CDT Wed May 23 2018

Unseasonably warm and humid conditions will be the story for the
holiday weekend as a stagnant upper level pattern keeps a warm
airmass in place. Chances for thunderstorms remain low and
centered primarily on the Friday timeframe.

Thursday builds on the warming trend that commences today under a
building upper level ridge. Widespread highs in the mid to upper
80s expected, while dewpoints in the lower 60s keep humidity in

Friday, an upper level shortwave originating out of the Northern
Rockies pushes through the northern periphery of the upper ridge,
sending a round of forcing through the area. Without any
discernible synoptic boundary expected at the surface, confidence
remains low and convection will be somewhat dependent on remnant
boundaries from nocturnal convective complexes focused to the
west. Based on this, SPC has a marginal threat for severe storms
with large hail and damaging wind over the northwest half of the
forecast area. Temperatures are again expected to reach well into
the 80s, while a more southerly flow drives dewpoints into the mid
60s for increased humidity.

Memorial Day Holiday weekend: A blocking upper level pattern will
keep the warm and somewhat humid airmass in place with highs in
the 80s, possibly reaching 90 and overnight lows in the 60s. There
remain slight chances for thunderstorms nearly each period, but
forecast confidence remains low throughout.

This pattern begins to break down by the middle of next week,
suggesting increasing chances for more widespread precipitation
systems, but continued well above normal temperatures.


.AVIATION...(For the 18Z TAFS through 18Z Thursday Afternoon)
ISSUED AT 1255 PM CDT Wed May 23 2018

VFR conds through this taf cycle with southeast winds less than
10 knots.




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