Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 241921
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
321 PM EDT Tue Apr 24 2018

LATEST UPDATE...
Synopsis/Short Term/Long Term/Marine/Hydro

.SYNOPSIS...
Issued at 321 PM EDT Tue Apr 24 2018

High temperatures from the 50s to near 60 are expected the rest of the
week compared to normal highs of lower 60s for this time of year. Scattered
rain showers this afternoon and evening will exit the area Wednesday
morning.

Another chance of rain showers arrives late Thursday night and Friday
with a cold front which ushers in a cool air mass for the weekend,
again keeping highs in the 50s. Above normal temperatures into
the 70s are then expected early next week.

&&

.SHORT TERM...(This evening through Thursday)
Issued at 321 PM EDT Tue Apr 24 2018

No impact weather is expected and no changes from the previous forecast.
Main concern in this time period is precipitation trends today and
tonight.

Agree with previous forecaster that activity should increase this
afternoon and evening. At 2 PM EDT a cold front extended roughly along
a Duluth, Minnesota to Omaha, Nebraska line. A strong attendant upper
PV anomaly seen on water vapor imagery. This feature will intensify
as it cross Lower MI overnight. Precipitation over Central Lower MI
appears to be associated with mid-level fgen and should become heavier
as fgen increases ahead of the PV max. This feature will be displaced
eastward by the PV maximum and that should be an end to the rain. However,
some of the convection allowing models suggest that sprinkles will
be possible up around US-10 later in the morning behind the cold
front.

As noted previously afternoon cloud development could be substantial.
As winds shift to a northwest direction in the afternoon, temperatures
will stay chilly by the lakeshore from Grand Haven southward (that
is, where the lakeshore is more northwest-facing).

Thursday looks quieter with less wind and clouds.


.LONG TERM...(Thursday night through Tuesday)
Issued at 321 PM EDT Tue Apr 24 2018

A mid level trough will be dropping down from the northwest to start
the period. One shortwave associated with this feature arrives in the
Great Lakes region Thursday night into Friday morning. Overall this
feature is shown to be weakening with time. Enough moisture and
lift are forecasted to support some shower activity which I will
keep in the forecast.

The next mid level vort max arrives Friday night. There are some differences
with the models. The High Res Euro is further south...tracking the system
close enough to the area to support some precipitation. The GFS is north
and would keep it dry. Will feature only low POPs for this potential
system for parts of the region. Temperatures at 925 mb from the High
Res Euro are positive through most of the night. That would limit the
risk for snow if this more southern track verifies. A cooler than normal
pattern sets up for the weekend behind this system.

Big warmup early next week. Deep warm air advection and the arrival
of a thermal ridge supports well above normal temperatures. I did nudge
temperatures up somewhat over the forecasted guidance.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 142 PM EDT Tue Apr 24 2018

Challenging forecast for the TAF sites today. Currently the
moisture moving into the area has been battling the dry airmass
that we have been in the past few days. Based on trends in the
observations and model data...it appears that the moisture will
continue to increase today...resulting in fairly continuous MVFR
with local IFR developing. Even for KGRR...there are indications
that a fairly large area of rain may develop overhead...which
could drive down the ceilings and possibly visibilities this
afternoon. Once the low conditions develop...they will gradually
move out from NW to SE later tonight and Wednesday morning.

&&

.MARINE...
Issued at 321 PM EDT Tue Apr 24 2018

Timing of current small craft advisories look on track and no changes
are planned.

&&

.HYDROLOGY...
Issued at 321 PM EDT Tue Apr 24 2018

With no significant precipitation expected, river stages will
continue to fall and the 5 current advisories should be able to be
dropped relatively soon.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory from 8 PM this evening to 8 PM EDT
     Wednesday for LMZ848-849.

     Small Craft Advisory from 2 AM Wednesday to 2 AM EDT Thursday
     for LMZ844>847.

&&

$$

SYNOPSIS...TJT
SHORT TERM...TJT
LONG TERM...MJS
AVIATION...MJS
HYDROLOGY...TJT
MARINE...TJT



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