Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 260455

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1155 PM CDT Thu May 25 2017


Issued at 305 PM CDT Thu May 25 2017

After morning overcast skies especially in our eastern half of
the cwa, skies have been mostly sunny this afternoon. 2 pm
temperatures ranged from the mid 60s to around 70 with light
winds. High pressure ridge was over the cwa providing the pleasant
day. However, on the return flow in the Plains, warm air
advection mid level clouds were spreading into far western MN and
western IA. Readings were well into the 80s to lower 90s from
western KS into TX.


.SHORT TERM...(This Evening through Friday)
ISSUED AT 305 PM CDT Thu May 25 2017

Forecast focus on chances for showers and storm returning.

Tonight: As the ridge shifts to our east, the return flow around
the high will spread warm air advection mid level clouds from west
to east across the cwa. In addition, the models indicate a few
showers or sprinkles developing, mainly after midnight. However,
forecast soundings indicate the low levels quite dry so much of
this will be virga. What does manage to reach the ground should be
a trace to .01, enough to dampen the cement. With the increasing
clouds and southeast winds, this will be a milder night. Lows
should bottom out in the mid 50s at most locations.

Friday: Models sweep a mid level weak wave in the WSW flow ahead
of a deepening trough in the northern Plains. The most aggressive
model is the GFS depicting a weak surface low tracking across our
far se cwa. Most of the models do not show a surface reflection.
The ESRL HRRR/HRRR/NAMNEST bring scattered showers and thunderstorms
into eastern IA/northeast MO mainly in the morning, then across
our IL counties in the afternoon. Deep layer shear is moderate
with MUCAPES of about 1000 J/KG, but will depend on amount of any
sunshine. SPC has a marginal risk of severe wind and hail roughly
near and east of the MS River during the afternoon. Maximum
temperatures should push into the 70s, which is what the
superblend suggests. Interestingly, the MAV has readings about 7 degrees
cooler suggesting a cloudier day, so this will need to be monitored.

.LONG TERM...(Friday Night through Thursday)
ISSUED AT 305 PM CDT Thu May 25 2017

The long term will feature mainly unsettled weather for much of the
Memorial Day weekend into early next week, including a chance of
severe weather for Saturday.

Friday night...After the passage of the mid-level vort max during
the day Friday, look for a break in precipitation to occur across
the region Friday night as showers and storms exit the region to the
east. It will be a muggy night with low temperatures and dewpoints
near 60.

Saturday...Will start off dry with a mix of clouds and sunshine
before potential for showers and thunderstorms increases by the late
afternoon and evening.

A trough currently over the far western US will move eastward and
reach the Plains and Midwest by Saturday afternoon/evening. Ahead of
this trough, all models are attempting to develop a surface low
pressure over Oklahoma with a warm front extending northeast into
the middle Mississippi Valley. However, models continue to have
disagreements on the placement of the warm front. The latest NAM and
GFS have joined with the GEM and the Euro in keeping front further
south. It is worth noting, however, that the GFS and NAM now have an
inverted trough moving across our area Saturday evening, but this
is likely due to convective contamination.

The position of the warm front will be a critical factor in
determining the threat of severe thunderstorms. Right now, the SPC
has a marginal risk of severe thunderstorms for the entire CWA, with
the exception of the far south being inside a slight risk. If the
warm front were to move north of our area, environmental parameters
including deep layer shear 40-50 kts, MUCAPE > 1500 J/kg and
conditionally unstable mid-level lapse rates would advect northward,
and would help support large hail and damaging winds as the primary
threats with thunderstorms. If the warm front were to remain south,
this would keep much of the severe threat towards the I-70 corridor
and points south. However, isolated large hail would be possible
with elevated storms that develop north of the front.

Please stay tuned for updates to this forecast.

Sunday through Tuesday...An upper level low associated with the
aforementioned trough will move south into the upper Mississippi
Valley by Sunday. This low will produce similar weather to what we
experienced earlier this week, with mostly cloudy skies and off and
on rain showers expected as pockets of moisture and weak shortwaves
round the low. This low will briefly park itself over the upper
Great Lakes, and will keep this pattern in place through Tuesday.
Expect temperatures to be below normal for the period as cool
northwesterly flows dominate. High temperatures are expected to
climb into the upper 60s to near 70.

Wednesday and Thursday...Upper level ridging and surface high
pressure will build across the Mississippi Valley beginning
Wednesday, bringing highs into the middle 70s. However, have low
pops as uncertainty exists due to the GFS and GEM attempting to
bring a shortwave into the region.


.AVIATION...(For the 06Z TAFS through 06Z Friday Night)
ISSUED AT 1153 PM CDT Thu May 25 2017

Mid-level clouds with isolated sprinkles or light showers will be
on the increase overnight. Coverage and impact too low to include
in TAFS. Scattered showers and a few thunderstorms are expected
to increase in coverage Friday morning into the afternoon from
west to east, with mainly low VFR ceilings. Have framed a 4-hour
window at each site when rain is most favored. Late afternoon
development may be just to the east of KMLI/KBRL.


Issued at 1123 AM CDT Thu May 25 2017

This morning we have upgraded Fulton and Gregory Landing from flood
watches to flood warnings as confidence has increased that these
locations will reach flood stage beginning early next week. Bellevue
remains in a flood watch as forecasts continue to keep this location
just at or below flood stage. We will continue to monitor this
location for any changes, including a possible upgrade.

All other locations along the Mississippi, with the exception of
Keokuk, remain under a flood warning. For the latest height
forecasts and trends, please see the latest flood statements.




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