Scientific Forecaster Discussion
fxus63 klot 260717
Area forecast discussion
National Weather Service Chicago/Romeoville, Illinois
217 am CDT Thu Apr 26 2018
210 am CDT
Another quiet weather day is in store across the area as a surface
and mid-level ridge slowly exit to the east. Expect mostly sunny
skies this morning to give way to filtered sunshine this afternoon
as widespread cirrus spread across the area. Temps today will be a
few degrees warmer than on Wednesday, with mid to upper 50s along
the immediate Lake Michigan shore to the mid 60s inland.
Additionally, with rather dry conditions aloft, daytime mixing
should produce minimum relative humidity values of 25-30% across much of the
A cold front and associated mid-level trough axis extending from
Hudson Bay to the Central High plains will track southeastward
across the County Warning Area during the early morning hours Friday. Given a very
dry antecedent air mass and limited deep forcing, only some very
isolated light showers/sprinkles are expected for an hour or two
along the front. Otherwise, conditions will be mostly cloudy with
north-northwest winds gusts of 20 mph to possibly 25 mph overnight.
309 PM CDT
Thursday night through Wednesday...
Overview...after a couple of cold fronts, a Summer-like warm up is
expected early next week.
A cold front moves through the forecast area Thursday night, and
guidance continues to back off on how much precip will accompany the
front. I lowered precip chances to slight chance, and i'm not
expecting much rain.
Another cold front and weak low pressure system move through Friday
afternoon/night, and the low could bring a better chance of rain
possibly storms. Precip is possible northeast of a Dixon to
Rensselaer, in line with the best chances over the Chicago Metro. I
kept thunder chances confined to over Lake Michigan, but there's a
low chance that an isolated thunderstorm could occur over the Metro.
Cooler temperatures follow both cold fronts, especially the second
front Friday. On-shore flow will keep Lakeside temps cooler Friday
through the weekend. The coolest day looks to be Friday with lake
side temps in the 40s, and highs in the 50s away from the lake.
High pressure shifts east allowing gusty south winds bring warmer
air to the region early next week. I bumped up high temps, but kept
them lower than what raw model guidance would suggest. 70s are
likely Monday and 80s are possible Tuesday. Increasing cloud cover
may limit warming Tuesday.
Showers and storms are possible mid week, and the European model (ecmwf) is quicker
to bring showers into the forecast than the GFS.
for the 06z tafs...
VFR conditions are expected through this evening at all sites. Light
winds will become SW less than 10kts this afternoon as a surface
ridge shifts to the east. A lake breeze may move far enough inland
to briefly reach mdw early this afternoon before increasing SW winds
push the lake breeze east of the terminal by late afternoon. A cold
front will then reach rfd late this evening and Ord/mdw during the
early overnight hours Friday, bringing a period of gusty north winds and
MVFR ceilings. An isolated -shra will be possible for an hour or two
with the cold front passage.
309 PM CDT
North winds will continue to diminish through this evening as
high pressure builds overhead. High waves and hazardous conditions
for small craft in the Illinois and Indiana nearshores will
continue into this evening. After brief southwest winds Thursday,
another cold front will drop over the lake Thursday night with a
push of north winds to 25-30 kt behind it. Yet another cold front
will push through Friday night, though with weaker northerly winds
behind it. Winds become south Sunday into next week. Small Craft
Advisory conditions are probable in the Illinois and Indiana
nearshores during the days Monday-Wednesday with gusty offshore
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