Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Chicago/Romeoville Illinois
555 am CST Thursday Nov 27 2014

Short term...
337 am CST

Through Friday...

Those dreaming of a white Thanksgiving will likely need to be
downwind of the lake along the Indiana and Michigan shores
today...although during the predawn hours there have been several
stations reporting persistent flurries but no accumulation on the
Illinois side as well. Afternoon highs likely will top out a few
degrees cooler than what would be more typical for Christmas than
late November...so even in areas that do not receive snow it will
still be quite a cold Thanksgiving.

Perhaps the most welcome news comes on Friday into the weekend when
temperatures should finally climb back into normal ranges...and
likely well above. Cold northerly flow ahead of an approaching high
is what will be keeping the lid on temperatures today...but winds
turn south by Friday and start to push the cold air away to our
northeast as the high drops into the Ohio Valley.

Lenning

&&

Long term...
337 am CST

Friday night through Thursday...

With weak to moderate warm advection late Friday into Friday
night and Saturday...temperature trends overnight could be flat to
slowly rising. Warm advection then develops in earnest during the
day Saturday ahead of a center of low pressure sliding across the
northern Continental U.S. And into the northern Great Lakes by Saturday
night.

As the northern lakes low lifts into Ontario and Quebec on
Sunday...a trailing cold front makes its way across the local area.
Aside from the areas getting lake effect snow today...this frontal
passage likely brings the best chance of precipitation over the next
few days...and right now there only appears to be a chance or slight
chance...primarily in the southeast part of the area. The European model (ecmwf) and
NAM are slower than the GFS with the progression of this
feature...so by leaning toward those solutions we allow at least the
southern portions of the area to experience another mild late
November day before the cold air returns for early next week.

With quasi zonal flow in place aloft next week and a progressive
pattern at the surface...the sharp Post frontal cooldown late Sunday
into Monday likely will evolve into another brief warmup above
freezing on Tuesday and Wednesday...though not as warm as this
weekend and maybe not even quite up to typical highs.

Lenning

&&

Aviation...

//Ord and mdw concerns...updated 12z...

* scattered flurries or light snow over the next several
hours...but with no visible restriction.

* MVFR ceilings returning later this morning...lasting through middle
day.

Rodriguez

//discussion...updated 12z...

Lake effect snow showers as well as MVFR ceilings have since
pushed east of all of the terminals...with the exception of gyy
where these are both still occurring. VFR ceilings in place for
the remainder of the terminals...as a passing middle level
disturbance is helping to provide scattered flurries or light
snow. These flurries/light snow will occur over the next several
hours...but with no real visible restriction or accumulation expected.
Upstream and to the west/northwest of the terminals...MVFR
ceilings still currently reside. Still expect these MVFR ceilings
to push east reaching the terminals this morning...with latest
short term guidance still supporting this. Am not too confident
with exact timing or duration...with these lower ceilings possibly
not arriving until later than in the tafs. Ceilings will improve
later this afternoon before shifting to the east...leaving VFR
conditions for the remaining forecast period. Northwest winds will
increase through this morning and middle day...with lighter winds
expected tonight as high pressure moves across the region.

Rodriguez



//Ord and mdw confidence...updated 12z...

* high confidence with flurries/light snow and visible this morning.

* Medium confidence of MVFR ceilings returning...and exact
timing/duration.

Rodriguez

//outlook for Ord/mdw for 00z Saturday-12z Thursday...updated 12z...

Friday night...VFR.

Saturday...VFR.

Sunday...slight chance of rain.

Monday...VFR.

Tuesday...slight chance of light snow late.

Wednesday...slight chance of light snow.

Rodriguez

&&

Marine...
424 am CST

Frontal boundary pushing down the lake early this morning and as
this is occurring...northwest winds are rapidly increasing up to
30 knots. This trend will continue in the near term with all areas
across the open waters observing northwest 30 knots winds today.
Although it does appear to be brief...occasional gale force gusts
still appear to be possible today and so have continued the
mention in the open waters forecast. For the nearshore
today...northwest winds will prevail with the strongest likely
observed in the Indiana nearshore. This is already occurring and
so have started the Small Craft Advisory for Indiana now and then extended it
further into tonight...as higher waves will linger for most of
tonight. After a brief lull in speeds tonight as high pressure
moves across the region...winds will turn to the southwest and
south on Friday. Southerly winds are expected to increase over the
lake and nearshore waters...with speeds up to 30 knots likely over
the open waters Friday and Friday evening. There once again
appears to be a possibility for speeds approaching gale
force...especially in the afternoon and early evening over the
entire lake. Have made mention of gale force gusts once again
during this time...but confidence of these higher speeds is low.
Will need to monitor these periods...with the possibility of these
higher speeds being observed.

Rodriguez

&&

Lot watches/warnings/advisories...
Illinois...none.
In...none.
Lm...Small Craft Advisory...Indiana nearshore waters until 4 am Friday.

Small Craft Advisory...lmz740-lmz741-lmz742...9 am Thursday to 6
PM Thursday.

&&

$$

Visit US at http://weather.Gov/Chicago (all lowercase)

Follow US on facebook...twitter...and youtube at:
www.Facebook.Com/nwschicago
www.Twitter.Com/nwschicago
www.Youtube.Com/nwschicago

National Weather Service Glossary of Abbreviations