Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 151814

Area Forecast Discussion
National Weather Service Quad Cities IA IL
114 PM CDT Sat Jul 15 2017


Issued at 315 AM CDT Sat Jul 15 2017

Amazing that the stratus from yesterday was still hanging on early
this morning, but has continued to dissipate. GOES-16 CH 14-11.20um
shows the stratus only covering Whiteside county in nw IL. Otherwise,
the remainder of the cwa had clear skies.

Temperatures at 3 am ranged from the mid 50s to lower 60s.

Water vapor movie loops indicated a short wave trough in
ND/northern MN vicinity moving southeast. A weak cold front was
moving across ND with a warm front that extended from the extreme
eastern Dakotas to northeast MO.


.SHORT TERM...(Today and Tonight)
ISSUED AT 315 AM CDT Sat Jul 15 2017

Forecast focus on thunderstorm chances tonight.

Today: Warm front will push across the cwa with warmer and more
humid conditions in the wake of the front. With a lack of a
trigger no convection is expected and in fact there should be
plenty of sunshine. Highs will push into the 80s and dewpoints
will be rising during the day, reaching around 70 in our nw cwa
this afternoon. No doubt it will be noticeably more humid later
today, compared to the past couple of days.

Tonight: SPC has a slight risk of severe storms barely dipping
into our far north near Highway 20. A marginal risk extends
southward to about Highway 30. There is low confidence that severe
weather will occur in the dvn cwa, with the better opportunity in
Wisconsin. However, still can`t rule out an isolated strong/severe
storm or two with gusty winds and hail late this evening into the
overnight hours in our north.

Models indicate the better forcing remaining to our north as a
short wave trough slides across the upper Midwest and Great Lakes.
Our northern cwa does get grazed by some weak forcing late this
evening and into the overnight hours, as a weak cold front arrives.
Forecast soundings indicate bulk shear about 30 knots and steep
mid level lapse rates around 7.5c/km. I favor the NAMNEST/ESRL HRRR
which shows a weakening line of isolated/scattered storms arriving
to the Highway 20 corridor towards midnight, and then sliding off
to the east across northwest IL overnight. Locations along and
south of Interstate 80 should remain dry due to the forcing north
of that area. Pops have been kept in the 20-30 percent range for
now. This will be a milder night ahead of the front, with lows in
the mid to upper 60s.

.LONG TERM...(Sunday through Friday)
ISSUED AT 315 AM CDT Sat Jul 15 2017

High pressure rebounding over the upper Great Lakes pushes a cool
front and the potential for thunderstorms south out of the area
Sunday. The ensuing northeast to easterly flow that follows will
lead to a dry period with relatively low dewpoints and near normal
temperatures Sunday night into Monday. Hot and humid weather and
periodic chances for thunderstorms then returns by mid to late in
the week as a ring of fire pattern redevelops.

Sunday into Monday, will maintain slight chances for afternoon
thunderstorms along the frontal boundary that will be pushing south
across far southeast IA, northeast MO and west central IL Sunday
afternoon. Current model timing of the boundary and the NAM nest
convective model would suggest this convective initiation may not
occur until the front drops south of the area. Northeast to east
surface winds that follow in the afternoon will slowly drive out the
initial humidity resulting from dewpoints pooling initially in the
60s to possibly lower 70s. Dewpoints lowering into the 50s over much
of the area will lead to another cool night with lows ranging from
the mid 50s northeast to mid 60s southwest, which will least
influenced by the Great Lakes high. This airmass lingers through
Monday with forecast highs in the upper 70s to near 80 in northwest
Illinois possibly too warm. Much further from the high, portions of
southeast IA and northeast MO will likely reach well into the 80s
under a developing warm air advection regime by afternoon.

Tuesday through Friday, an upper level high and dome of hot air sets
up over the central plains with the forecast area perched along the
northeast periphery, setting the stage for an extended period of
very warm temperatures, high humidity and daily chances for
thunderstorms along wavering boundaries. Model blends place highs
generally in a range from the upper 80s northeast to the lower 90s
south and southwest through the period. These highs will of course
be dependent on timing and coverage of thunderstorm complexes
throughout, which are handled with slight to low chance pops. With
dewpoints returning to the 70s, afternoon and early evening heat
index values may reach near or above 100, especially Wed and Thu.
These high dewpoints will also lead to some warm nights, with Tue
night and Wed night possibly seeing mins only in the 70s.


.AVIATION...(For the 18Z TAFS through 18Z Sunday Afternoon)
ISSUED AT 108 PM CDT Sat Jul 15 2017

Main concern in this forecast period is thunderstorm chances
associated with the shortwave trough moving across the upper
Midwest. Model consensus suggests weakening line of storms moving
into the north late this evening and overnight, and this looks
reasonable. Thus will have a chance group at DBQ but not elsewhere
given uncertainty. MOS guidances also suggests fog and low
clouds, but GFS is too high with dew points and figure this may be
biased guidance too moist.




LONG TERM...Sheets
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