Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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000
FXUS63 KGRR 260104
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
904 PM EDT Sun Oct 25 2020

LATEST UPDATE...
Update

.SYNOPSIS...
Issued at 330 PM EDT Sun Oct 25 2020

-A few light showers possible through Tuesday, chilly

-Sunny and breezy Wednesday, slightly warmer

-Chance of rain Thursday, mainly south

&&

.UPDATE...
Issued at 855 PM EDT Sun Oct 25 2020

The latest trends in radar and model data suggest an earlier
arrival of the light precipitation tonight and a higher potential
for central parts of the CWA. As a result we bumped up POPs for
later tonight. There was an area of FGEN over in WRN IA with an
expanding area of precipitation in that region as of 01z. The
latest HRRR...NMM and RAP13 suggest that feature and associated
precipitation will make it into the BIV to GRR to AMN region later
tonight into early Mon.



&&

.DISCUSSION...(This evening through next Sunday)
Issued at 330 PM EDT Sun Oct 25 2020

-- A few light showers possible through Tuesday, chilly --

Strong swly upr level jet stretching from the southwest U.S. to
the GrtLks Rgn will continue to send considerable cloudiness our
way through Tuesday. The clouds will hold high temps in the 40s.
Chances of rain are not the greatest due to dry air in the lower
levels.

The best chance of light showers tonight and Monday is around
Ludington based on extrapolation of upstream precip as well as
location of best divergence aloft related to a coupled jet
structure aloft. There is also the possibility of a northerly flow
lake effect band impacting this area. Still can`t rule out a few
snowflakes mixing in, mainly in the overnight to early morning
period when coolest sfc temps are present.

On Tuesday whatever remains of that lake effect band should move
more onshore as the low level flow turns westerly, but will
probably dissipate as it does so.

-- Sunny and breezy Wednesday, slightly warmer --

Model RH progs continue to suggest a sunny day on Wednesday but a
tightening pressure gradient between a sfc high to our south and
a sfc low tracking east toward Hudson Bay should result in breezy
conditions developing. Gusts to 25 mph from the southwest appear
likely but that flow also pushes in slightly warmer air with highs
of 50-55 expected.

-- Chance of rain Thursday, mainly south --

Tropical Storm/Hrcn Zeta will be lifting north from the Gulf mid
week as the upper low ejects east/northeast from TX.
Deterministic and ensemble guidance has been indicating the
possibility of the deformation zone of this merging system
impacting srn Lwr MI - at least the nrn fringes.

Our model blend currently has low chance pops from I-96 south
Thursday, but if a more northern trend develops, pops will need
to be raised and expanded north of I-96.

Once that system goes by it looks dry with a warming trend. Highs
next weekend may get well into the 50s with dry conditions for
Halloween.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 729 PM EDT Sun Oct 25 2020

The main change to the aviation forecast was to move up the timing
of the showers and associated impacts. Recent trends show an area
of rain developing in IA and NE that was moving northeast. As this
rain moves in later tonight...ceilings and visibilities will lower
into the MVFR category. Out ahead of this rain...there were MVFR
clouds around KJXN. Those may expand with time...especially as the
rain nears. The MVFR conditions will likely linger into Monday and
in some cases through much of the day.


&&

.MARINE...
Issued at 330 PM EDT Sun Oct 25 2020

It now appears that the northerly flow on Monday may increase
substantially in the afternoon and lead to conditions hazardous
to small craft. The other timeframe of concern is late Tuesday
night into Wednesday when strong southwest flow should also result
in hazardous conditions.


&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...None.
&&

$$

UPDATE...MJS
SYNOPSIS...Meade
DISCUSSION...Meade
AVIATION...MJS
MARINE...Meade



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