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686 
FXUS63 KGRR 160018
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
818 PM EDT Mon Apr 15 2024

.KEY MESSAGES...

- Showers and Storms Tuesday Night into Wednesday Night

- Light Rain Chances Thursday Night

- Cool Down for the End of the Week

&&

.DISCUSSION...
Issued at 339 PM EDT Mon Apr 15 2024

- Showers and Storms Tuesday Night into Wednesday Night

Quiet weather will persist tonight and most of if not all of
Tuesday as high pressure drifts through the region. A warm front
approaches from the southwest late in the day on Tuesday and moves
squarely into the forecast area Tuesday night. The surface low 
associated with the front will swing across the forecast area on 
Wednesday with a warm sector likely pushing into southern portions
of the forecast area in the midday to afternoon hours. The active
weather is very much centered in the Tuesday night and Wednesday
forecast periods.

Tuesday looks to be dry with showers and likely embedded
thunderstorms moving in Tuesday evening. Forecast most unstable
CAPE values are not significant Tuesday night in the 400-800 j/kg
range. Expecting periods of rain with some rumbles of thunder
embedded. Not expecting severe weather and the SPC agrees with a
general thunder forecast.

Wednesday could be a bit more interesting, but there are caveats
with that statement. We are expecting a good amount of clouds and
rounds of precipitation Tuesday night lasting into Wednesday
morning. The clouds and rain will keep instability levels down a
bit, but the 3km NAM is showing 1,000-2,000 j/kg of most unstable
CAPE developing. a 30+ knot low level jet combined with a 40+ 
knot mid level jet produce deep layer shear around 40 knots
towards I-94. Expecting more rounds of showers and storms on
Wednesday, but with the chance of a few stronger storms. The way
Wednesday could over perform (severe weather) is if the 
precipitation is a bit less coming into Wednesday and we get areas
of clearing in spots. Deep layer shear of 40 knots combined with 
1,000+ j/kg of MUCAPE could certainly produce some severe weather.
Multiple fronts in the area and the potential for rotating storms
has our attention if the above caveats of less precipitation and 
clouds come to fruition. The issue with severe chances on 
Wednesday is less precipitation and clouds is not a good bet at 
this time. Agree with the SPC marginal and we will see how things 
evolve. With tonight's model runs the event will be fully in the 
HREF window which is obviously the gold standard in terms of 
convective model forecasts. Showers move off to the east Wednesday
night as the low pulls away. 

Rainfall totals look to be around an inch from this system which
should push a few sites to near or slightly above bankfull. That
said, we are not expecting much in the way of flooding issues.

- Light Rain Chances Thursday Night

A cold front will move through the area Thursday night to Friday 
morning bringing renewed chances for light rain. Conditons should 
turn dry after daybreak Friday as the front moves east. HIgh 
pressure slides in behind that front resulting in dry conditions 
through the weekend. Skies will begin to clear out Friday morning 
with good chances for sunshine Friday afternoon through Monday. 

- Cool Down for the End of the Week

The surface low that tracks through the area Tuesday and Wednesday 
moves northwards into the Hudson Bay area on Thursday. 850mb thermal 
trough settles in over the region on the backside of the low with 
prolonged cold air advection through the weekend. 850mb temps bottom 
out around -3C to -6C Saturday, resulting in peak afternoon surface 
temps in the 40s to 50s. High pressure brings clearing skies this 
weekend with radiational cooling dropping overnight temps to 
freezing Saturday night and Sunday night.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 820 PM EDT Mon Apr 15 2024

VFR ceilings and visibilities will continue through the forecast 
period with dry conditions. Winds will shift easterly between 00z 
to 06z, and will increase after 12z Tuesday. Easterly winds of 
10 to 15 knots are expected late Tuesday morning, early Tuesday 
afternoon winds will increase with gusts up to 20 to 25 knots. 
Wind will continue through Tuesday evening as a system producing 
rain showers and storms moves through the area.


&&

.MARINE...
Issued at 339 PM EDT Mon Apr 15 2024

A light wind regime will continue for the area tonight. High
pressure will remain in control one more forecast period before
things become more active. The ridge of high pressure moves off to
the east on Tuesday allowing for a strengthening easterly flow to
develop. 15 to 20 knot winds in the morning will be sub advisory,
but in the afternoon wind speeds increase. A small craft advisory
based on wind speeds will be needed for Tuesday afternoon, but an
increase to gales in the nearshore is possible. At this point
planning on holding off given offshore winds and borderline gales.
Envision the night shift will make the call on SCA vs Gale.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.

&&

$$

DISCUSSION...Duke/Thielke
AVIATION...Ceru
MARINE...Duke