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FXUS63 KDVN 091051 AFDDVN

Area Forecast Discussion National Weather Service Quad Cities IA IL 451 AM CST Sat Dec 9 2023

KEY MESSAGES

- Rain will be ending this morning.

- Brisk/windy by afternoon through this evening and colder.
Gusts over 25 mph to 30 mph likely (60-80%).
Chance (20%) of rain/snow showers, mainly along/north of I-80.

- Seasonable to above normal next week, and generally dry until heading into next weekend.

SHORT TERM /THROUGH TONIGHT/
Issued at 255 AM CST Sat Dec 9 2023

This morning

A shortwave trough is currently lifting through the region along with an attendant open wave surface cyclone over west central Illinois. This cyclone will gradually deepen while riding up along a cold front bisecting the area. Upper diffluence, and low to mid level frontogenetical forcing along a baroclinic zone will continue to foster high coverage of rain in the pre-dawn hours.
However, the forcing looks to quickly wane along with the rain chances from SW to NE by 12z to 15z as the wave departs and a dry slot works into the area. The dry slot and subsidence is likely (60-80%) to foster a break-up of cloud cover and allow for at least partial sunshine to return prior to midday in many areas. Temperatures will fall through mid morning with initial cold advection in the wake of the exiting cold front, before readings level off and/or rise a bit with the solar insolation.

This afternoon and tonight

A secondary and stronger cold front, situated upstream along the Dakotas/MN border into northwest IA early this morning, will sweep across the area into this evening. Steep low level lapse rates and cold advection will foster a ramping of W/NW gusts of 25-35 mph and lead to another gradual downward slide on temperatures into the 30s most areas by early to mid evening. Wrap-around/cyclonic flow will slosh widespread low clouds into the region. Forecast soundings show sufficient moisture depth and weak instability for a few rain to snow showers (20% chance), mainly along and north of I-80 within the better cyclonic vorticity advection. Impacts should be minimal and mainly focused on brief visibility reductions, as air/ground temperatures near to above freezing and minimal measurable precipitation potential squelch any accumulations.

Wrap-around low cloudiness is likely to result in partly cloudy to cloudy skies tonight. As a result of the cloudiness and also persistent gusty winds, I favor a warmer guidance blend of 75th and 90th percentile of NBM for lows, roughly from the mid 20s portions of far west/southwest where some clearing can't be ruled out (30-50% chance) to the upper 20s to lower 30s elsewhere.

LONG TERM /SUNDAY THROUGH FRIDAY/
Issued at 255 AM CST Sat Dec 9 2023

Much of the period is looking seasonable and generally dry. The pattern aloft through mid-week looks to remain northwesterly.
Normally we'd be susceptible to below average temps in that flow regime this time of year, but air parcel trajectories point mostly toward western Canada into the Pacific Northwest as the source region which is currently under seige from a rather persistent Atmospheric River event. The anomalous moisture aided by an Aleutian low will mean temperatures not as cold, therefore we're likely (50-70%) to see temperatures near or even slightly above normal through mid-week.

Late in the week into next weekend there is signs of a trough emerging from the Southwest and into the central CONUS, though there's plenty of disagreement on track/strength in the deterministic models and ensembles. Nonetheless, a southwesterly flow ahead with a departing mid level ridge looks to promote above to much above normal temperatures during this time-frame, with NBM 75th and 90th percentiles indicating that some 50s would be possible to return for highs if everything lined up just right i.e. limited cloud cover, no precip, etc, as NBM for now has some chances (20-40%)
for precipitation (mostly rain).

AVIATION /12Z TAFS THROUGH 12Z SUNDAY/
Issued at 445 AM CST Sat Dec 9 2023

Rain will be ending at the river TAF sites at the start of the period.
Thereafter, VFR conditions are expected with increasing westerly winds turning gusty up to 25 kt by mid to late morning.

This afternoon into tonight, a secondary cold front will sweep through the terminals. This will be accompanied by stratus with predominantly MVFR ceilings of 1500-3000 ft agl and continued gusty W/NW winds up to 30-35 kt. Isolated rain/snow showers are also possible (20 percent chance). These may be accompanied by brief visibility restrictions.
The probability of occurrence at the TAFs is too low for any mention at this time, but this will be monitored. Overnight, a return to VFR is possible (30-50% chance) via partial clearing and/or lifting of ceilings, especially at KCID and KBRL.

DVN WATCHES/WARNINGS/ADVISORIES
IA...None.
IL...None.
MO...None.

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