Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 281118
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
618 AM CDT Thu May 28 2020

...12Z AVIATION UPDATE...

.SYNOPSIS...
Issued at 335 AM CDT Thu May 28 2020

Mild temperatures continue early this morning, with readings in the
upper 60s and lower 70s. Dewpoints were slightly higher than in
the previous 24 hrs and were in the upper 60s to low 70s.

06z MSAS surface analysis shows a weak low over central IA, with a
boundary extending northeast into southeast MN and south into
central MO. Dewpoints have been pooling ahead of the front in our
area. Morning water vapor imagery shows the cutoff low across the
south hasn`t moved much and is now near the OK/AR border. Radar
imagery showed an area of showers moving northwest from northwest IL
into WI and southeast MN.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 335 AM CDT Thu May 28 2020

Key Messages:

1. A flash flood watch has been issued for portions of the area
until 00z Friday. Heavy stratiform rain with embedded thunder will
bring a risk for flash flooding.

2. Cooler today with widespread rain impacting many hometowns.
Clearing skies and near seasonable temperatures overnight tonight.

Discussion:

Latest 00z guidance has come in wetter for today and with a better
synoptic forcing setup have opted to issue a flash flood watch
for areas west of a Dubuque county to Scotland county line. With
the 00z sounding from last night already showing PWs in the 94th
percentile or 178% of normal and more mid level moisture advecting
into the area, heavy rain is a sure thing today. Flash flood
guidance values are in the 1.5"/hr or 2"/3hr range for areas that
have seen rain in the past 3 days. 00z HREF and several CAMs
suggest that 2-3" rain in three hours is possible with this moist
environment and WPC has much of the area in a slight risk for
excessive rainfall today. Do not anticipate much thunder with tall
skinny CAPE profiles and weak mid level lapse rates and thus
widespread heavy rain showers with some embedded thunder is
expected. Better synoptic support with upper level divergence and
low/mid level convergence will bring more widespread rain today as
opposed to previous days. Model consensus has the weak cold front
just east of the MS RVR by 00z Friday with precipitation ending
from west to east during the evening.

Highs will be a challenge today with the clouds and rain. Have
lowered highs some more over the west where rain will be the
heaviest.

Tonight: Clearing skies and lower dewpoints will allow temperatures
to drop into the low to mid 50s. Northwest winds 5-10 mph overnight
should prevent any fog development.

.LONG TERM...(Friday through Wednesday)
ISSUED AT 335 AM CDT Thu May 28 2020

Key Messages:

1) Generally dry and pleasant through the weekend.

2) Warm-up next week with above normal temperatures.

Forecast details...

Friday-Sunday

Breezy NW winds and influx of cooler, drier air will make for a
notable and refreshing change on Friday from the recent stretch of
summer-like warmth and humid conditions. The pleasant temperatures
(near to slightly below normal) and lower humidity levels will
stick around through the weekend, as high pressure builds down
across the Upper Midwest and Great Lakes. A potential small
fly in the ointment is a low potential for some light showers
this weekend, mainly across far southeast Iowa and northeast
Missouri with proximity to mid level theta-e gradient and shortwave
energy shuttled down in northwest flow. More probable is just
some increase in clouds and perhaps sprinkles, with ridging and
dry air influx largely a deterrent against measurable rain prospects.

Monday-Wednesday

Early in the week will bring some return flow/warm advection shower
chances on the backside of the departing high. Models trending
toward a tighter pressure gradient and stronger SSW low level
flow on Monday, and will need to be monitored as this would
boost mixing heights and potentially necessitate a boost to the
going high temperature forecast as well (thermally supportive
of widespread upper 70s/lower 80s), though clouds/precipitation
dependent. Temperatures then look to remain above normal into
the middle of next week. The mid to late week time period does
offer considerable uncertainty, with two different scenarios...
1) active mid to late week with stalled boundary and rounds of
showers and storms (supported by GFS and ECM ensembles), or
2) transient rain chances tied to a frontal boundary mid week
then cooler and drier late week (supported by ECM deterministic
and GEFS). Due to the uncertainty no changes were made to the
NBM, which is toward the idea of an active stretch, with daily rain
chances mid to late week and seasonable temperatures.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday Morning)
ISSUED AT 613 AM CDT Thu May 28 2020

Patchy shallow dense fog with LIFR/VLIFR conditions will lift
over the next 1-2 hrs. In general, MVFR to IFR conditions look
to prevail today with periods of rain/showers and isolated storms
before a cold front moves through by late afternoon and evening
bringing an end to the rain. Winds will shift to the northwest
with the passage of the front, ushering in drier air leading to
an improvement to VFR.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Flash Flood Watch through this evening for Benton-Buchanan-Cedar-
     Delaware-Dubuque-Henry IA-Iowa-Jefferson-Johnson-Jones-
     Keokuk-Linn-Van Buren-Washington.

IL...NONE.
MO...Flash Flood Watch through this evening for Scotland.

&&

$$

SYNOPSIS...Gross
SHORT TERM...Gross
LONG TERM...McClure
AVIATION...McClure



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