Scientific Forecaster Discussion
fxus63 klot 230247
Area forecast discussion
National Weather Service Chicago/Romeoville, Illinois
847 PM CST Wed Nov 22 2017
847 PM CST
For evening update...
Minor tweaks to temps overnight, as cloud cover and a slight
increase in south-southwest wind overnight will keep temps from
falling off too much across the region. After a brief drop with
sunset with lighter winds and thinner cloud cover, temps have
steadied and should remain fairly close to current readings for
the remainder of the night. A few weak radar echoes have been
noted from mid-level clouds (11-12 kft), in association with mid
level speed Max translating southeastward across the region. No
precipitation is expected to reach the surface however, given very
dry air below about 600 mb in 00z dvn sounding. Mid-level trough
should be moving out of area by morning, setting the stage for a
dry and milder Thanksgiving day.
1242 PM CST
High pressure will move east of the area tonight with light
southerly winds developing. The combination of the light south
winds and more so mid-high level overcast should help keep temps
much milder tonight vs last night. Skies should clear out
Thanksgiving day with temps milder than today.
Thursday night into Friday, strong low pressure will track east
across southern Canada leading to increasingly strong southerly
winds Thursday night and especially Friday. Gulf of Mexico is shut
down for business with respect to moisture return, so with the
southerly winds only advecting recycled Continental air north,
stratus seems unlikely. Given the expected sunshine and strong
low level winds encouraging mechanical mixing of the warmer air
aloft to the surface, strongly suspect guidance temps aren't warm
enough Friday. The forecast 925mb temps Friday afternoon in the
ECMWF, GFS, and NAM all support highs reaching the lower 60s.
While i'm not comfortable going that warm yet, did adjust highs up
considerably from the blended initialization.
1242 PM CST
Friday night through Wednesday...
Main storm track through the long term period will remain well
north of our area, which should result in little if any precip
through the period and a temperature roller coaster. Cold front
will knock temps down some over the weekend, generally in The Ball
park of seasonal norms, before the next powerful cyclone develops
and results in more strong southerly winds and unseasonable warmth
early next week. Once again, forecast 925mb temps from the GFS and
European model (ecmwf) would support highs well into the 50s to near 60 Monday.
Nudged temps upward in that direction, but still likely far too
cool if current progs verify. Some differences arise between the
European model (ecmwf) and GFS heading into the middle of next week, but generally
near to above normal temps and dry conditions look to be the rule
at this point.
for the 00z tafs...
Fairly steady state conditions expected over the next 24-30 hours
across northern Illinois and Northwest Indiana. High pressure will
settle over the Ohio Valley tonight and tomorrow with southwest flow
and VFR conditions prevailing at the terminals. Low pressure is
currently in place over the Dakotas this evening and will move into
the upper Midwest tomorrow morning but will weaken as it does so. A
remnant cold front will move across northern Illinois late morning
and early afternoon. No precipitation will occur but the decaying
cold front will likely bring mid level ceilings and turn winds more
westerly for a few hours late in the afternoon before settling back
out of the southwest Thursday evening.
1242 PM CST
Active pattern expected on the lake the next week. First, as high
pressure moves east tonight, southerly winds will develop and
freshen up over night into Thursday. Gales look unlikely, but
winds could push 30kt for a time thurs morning over northern
portions of the lake. Southerly winds will really ramp up later
Thursday night into Friday as deep cyclone tracks east toward the
upper Great Lakes region. Guidance continues to support gale force
winds and will be hoisting a gale watch for the Open Lake for this
southerly wind event. Cold front will move across the lake Friday
night, but with only a modest push of cold air in the wake of the
front, the northwest winds will probably top out just below gales
Saturday. Another period of strong southerly winds and possible
gales look to be on tap for Sunday night into Monday.
Lm...gale watch...lmz777-lmz779...6 am Friday to 9 PM Friday.
Gale watch...lmz740-lmz741-lmz742-lmz743-lmz744-lmz745...9 am
Friday to 6 PM Friday.
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