Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 150540
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1240 AM EST Wed Feb 15 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 309 PM EST Tue Feb 14 2017

Rain will quickly transition to snow overnight with minor
accumulations expected mainly north of I-96. Wednesday will be
colder with highs generally around 30. Lake effect snow showers will
be common especially west of US-131, although additional
accumulations should be minor.

After seasonal highs near freezing on Thursday, a pronounced warm-up
will commence with highs well into the 50s over Southern Lower
Michigan. Very warm temperatures are expected to persist well into
next week. Dry conditions are expected from Thursday through at
least Sunday.

&&

.UPDATE...
Issued at 752 PM EST Tue Feb 14 2017

Updated the marine products to take out the SCA wording. Gale
gusts are accompanying the passage of the convective showers
associated with the cold front.

Will keep the winter weather headlines going. Heavier bursts of
precipitation associated with the front were resulting in pockets
of heavier snow showers and gusty winds...over 35 knots in some
cases. Looks like there will be a lull behind the front...but
deeper moisture is forecasted to return later this evening or
closer to midnight from the north. If this happens there could be
a period of steadier snow showers with a potential for impacts as
temperature will be below freezing by then.

UPDATE Issued at 720 PM EST Tue Feb 14 2017

Forecast was updated to mention the risk for a few thunderstorms
up north. Steeper low level lapse rates through the -20 combined
with better lift along the front was just enough to trigger the
storms.

&&

.SHORT TERM...(This evening through Thursday night)
Issued at 309 PM EST Tue Feb 14 2017

Have issued a winter weather advisory with the chief concerns being
slippery travel conditions and reduced visibilities. We are more
certain about this farther north around US-10. Accumulations are not
expected to be significant here or anywhere else and are of lesser
concern for this advisory.

Was very generous with extending this advisory south. Many areas
near and south of the I-96 corridor may end up with little if any
effects as we see plenty of situations when roads dry off the
precipitation well before reaching freezing temperatures. However,
there is at least some risk of reduced traction during the morning
commute which is the main reason for advising this far south.

For Wednesday, agree with previous forecaster that lake effect
showers should be pretty common west of US-131 for reasons I won`t
repeat here. May make minor adjustments downward in snow totals, but
this shouldn`t affect general expectations. Brief rapid changes in
visibility remain a concern primarily near the lakeshore, and
subsequent shifts may possibly decide to extend part of the advisory
into the afternoon. By early Wednesday night, residual lake effect
snow showers over far Southwest Lower Michigan should dissipate.

It`s worth noting as an aside that several model solutions question
moisture availability in the DGZ during this time. They generally
tend to underdo DGZ moisture with LES situations in general. We
especially notice this with the HRRR/HRRRX models, which developers
are currently investigating.

.LONG TERM...(Friday through Tuesday)
Issued at 309 PM EST Tue Feb 14 2017

Unseasonably warm conditions for late February will occur during the
extended period.  Southerly flow develops Friday as high pressure
moves to the east.  A weak frontal passage is expected Sunday but
precipitation is not expected and cloud cover may be hard to come by
due to lack of moisture.  A resumption of southerly winds Monday
into Tuesday will allow for even warmer weather to spread into
Michigan.

The mid level ridge axis passes overhead Monday afternoon...which
will allow deeper moisture to encroach the region and precipitation
chances to increase.

High temperatures will be in the upper 30s to middle 40s on
Friday...warming into the lower and middle 50s Saturday.
Temperatures will be slightly cooler on Sunday...from the upper 40s
to lower 50s.  The warmest day would be on Monday with highs
possibly approaching 60.  Low temperatures should be at or above
freezing for most locations each day.  For perspective...normal
highs for Grand Rapids are in the middle 30s.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1240 AM EST Wed Feb 15 2017

Northwest flow will extend through the day Wednesday. VFR and
MVFR conditions are expected primarily for cigs of 2500-5000 ft.
Snow showers will develop off Lake Michigan, but the setup is not
one that would indicate anything dominant. It is possible for
vsbys to temporarily drop within snow showers, mainly at western
TAF sites (KMKG, KGRR and KAZO). Gusty conditions up around 20kts
are expected to finally subside Wednesday evening.


&&

.MARINE...
Issued at 309 PM EST Tue Feb 14 2017

No changes to previous thinking. We are looking at a pretty
borderline gale warning with perhaps a few hours of gale force gusts
working south along the lakeshore overnight. Small Craft Advisory
waves will linger most of Wednesday. We will hold off on SCA
issuance for that until tonight when the cessation of gale
conditions becomes more predictable.


&&

.HYDROLOGY...
Issued at 133 PM EST Tue Feb 14 2017

River levels continue above normal, but minor flooding has come to
an end. Little precipitation is expected through the week and
temperatures will be above normal, so river levels should fall into
next week.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory until 9 AM EST this morning for
     MIZ037>040-043>046-050>052-056>059-064>066-071>073.

LM...Gale Warning until 7 AM EST this morning for LMZ844>849.

&&

$$

UPDATE...MJS
SYNOPSIS...TJT
SHORT TERM...TJT
LONG TERM...MWS
AVIATION...JAM
HYDROLOGY...63
MARINE...TJT



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