Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 201740
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
140 PM EDT Mon Mar 20 2017

LATEST UPDATE...
Aviation/Hydro

.SYNOPSIS...
Issued at 1134 AM EDT Mon Mar 20 2017

Precipitation is expected to exit the region early this evening.
Quiet weather is then expected for Tuesday and Wednesday. The next
chance of rain will hold off until Thursday night, but it appears
to linger into Saturday.

High temperatures will be around 50 today and Tuesday, then cooler
days are expected Wednesday and Thursday, mainly 40 to 45. We
will end the week warmer again with 50 to 55 expected for Friday
and into the weekend.

&&

.UPDATE...
Issued at 1132 AM EDT Mon Mar 20 2017

Have adjusted PoPs to feature Chance/Likely from the I-94
corridor southward. Latest radar and satellite images show surface
based thunderstorms growing in coverage over northwest IN and
moving east-southeast. Although this shouldn`t affect our forecast
area, we are monitoring an area of accas closer to the I-94
corridor that is becoming more vigorous ahead of a small upper PV
anomaly currently moving east across southern WI. Approximately
half of the available convection allowing models produce storms
over I-94 this afternoon while the other half keeps activity
displaced well to the south. This is indeed an either/or scenario
and seeing how the accas field evolves over the next couple hours
will be key.

&&

.SHORT TERM...(Today through Wednesday)
Issued at 330 AM EDT Mon Mar 20 2017

After a storm night with some small hail, a cold front will cross
the CWA this afternoon, bringing more showers and a few
thunderstorms.  This rain ends by early evening, leading to a quiet
period for late tonight through Wednesday.

The best jet dynamics has exited the region early this morning and
the showers and storms were weakening.  However with the front
crossing the area this afternoon we will see showers and a few
storms regenerate.  Some upper divergence moves over the southern
CWA by early afternoon too, helping support a better coverage of
pcpn there.  Enough elevated instability to expect scattered
thunderstorms too through about 21Z along and south of I-96.  there
could be a few lingering showers over the SE CWA into this evening,
otherwise the region begins to dry out.

A large area of cool and dry Canadian high pressure moves in for
Tuesday and Wednesday.  H8 temps drop to around -12C by Tuesday
night.  With the dry air mass expect a large diurnal temp swing.
Tuesday should be 45 to 50, then lows crash to 15 to 20 for Tuesday
night.  Highs Wednesday will recover to the 30s.  Despite the chilly
air, the air mass looks far too dry to support any lake effect.

.LONG TERM...(Wednesday night through Sunday)
Issued at 330 AM EDT Mon Mar 20 2017

One last cold night starts out the period with high pressure
positioned over the Great Lakes. This high will begin departing to
our southeast. As winds shift out of the south, temperatures will
gradually moderate through the day Thursday with highs returning toe
near normal.

We continue to see our next weather maker come ashore over the
southwestern conus in the same timeframe. The upper level trough
progresses eastward, developing into a closed low over the central
plains. The closed upper low, in conjunction with a deepening
surface low, will further strengthen warm air advection Thursday
night into Friday.

Showers are expected to develop late Thursday into Friday as the
warm front lifts north. The onset of the precipitation could fall as
a bit of rain/snow, but it is becoming a little suspect with web
build zero height jumping to 8-9k feet through midnight Friday.
Bufkit overview also seem to show surface temperature rising above
freezing. So we may be able to escape much or even all winter
precip...given these trends continue. High near 60 Friday are
looking more and more likely with the front lifting north of the
forecast area.

What happens beyond Friday begins to diverge with long range models.
The GFS takes the upper low further south with a weakening cold
front clearing Lower Michigan of precipitation by Sunday. This would
act as more of a slight cool down as ridging develops right behind
the system again. The ECM, however, take the upper low much further
north...right over the Great Lakes...keeping precip chances high
through the weekend. Either solution would keep temperatures near
normal.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 140 PM EDT Mon Mar 20 2017

Scattered showers and thunderstorms will be across far southern
Lower Michigan this afternoon near AZO...BTL and JXN. MVFR
conditions are expected until around 23Z. Elsewhere we expect VFR
to prevail. Southwest winds this afternoon will go northwest by
this evening and remain at or blo 10 knots.

&&

.MARINE...
Issued at 330 AM EDT Mon Mar 20 2017

We will probably need a small craft advisory by Tuesday evening and
lasting through the first half of Wednesday.  Northerly winds behind
the front will cause waves to build.

&&

.HYDROLOGY...
Issued at 140 PM EDT Mon Mar 20 2017

Generally 0.05 to 0.25 inches of precipitation fell Monday morning.
Scattered showers could produce similar amounts in portions of the
area this afternoon and evening. Flooding is not expected. Tuesday
through Thursday looks dry. Later this week and into next week,
there are indications of mild temperatures returning and several
rounds of showers and thunderstorms being possible.

&&

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

$$

UPDATE...TJT
SYNOPSIS...TJT
SHORT TERM...JK
LONG TERM...JAM
AVIATION...Ostuno
HYDROLOGY...CAS
MARINE...JK



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