Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 241735
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
135 PM EDT Mon Apr 24 2017

LATEST UPDATE...
Aviation/Hydro

.SYNOPSIS...
Issued at 324 AM EDT Mon Apr 24 2017

An area of high pressure will build into Ontario
today. This fair weather system will generate southeast winds here
in Michigan...drawing a dry airmass into the state.
A low pressure system will attempt to move in from the west on
Tuesday...but it will be slowing down. Thus it looks like any
chance for rain will hold off until Wednesday.

&&

.UPDATE...
Issued at 1029 AM EDT Mon Apr 24 2017

I updated our grids using the HRRR wind, temp and dewpoints with
the idea it would better capture the deep mixing expected today.
This does not change the forecast high but it lowers the RH and
allows a lake breeze which was not being (in my opinion) well
captured by the previous grid set today.

&&

.SHORT TERM...(Today through Wednesday)
Issued at 309 AM EDT Mon Apr 24 2017

The main trend in the short term period is for a delay to the
precipitation. Models are still trying to generate some showers
and thunderstorms for Tuesday. Right now the forecast soundings
look way too dry for this to happen. In addition there is an
inversion shown around 700 mb. Will keep them out of the forecast
for Tuesday because of these reasons.

Then on Wednesday...the trend is to keep the axis of better
moisture west of the CWA. Will lower POPs because of this trend.
The models are still showing some instability around...so will
keep the mention of thunder in the forecast. It will be quite warm
on Wednesday. I would not be surprised to see a few 80 degree
readings...especially toward the Battle Creek to Jackson region.

I did raise temperatures for areas near the lakeshore today and
Tuesday. The southeast to south flow commonly supports warmer
daytime values for locations generally along and west of highway
131.

.LONG TERM...(Wednesday night through Sunday)
Issued at 309 AM EDT Mon Apr 24 2017

The wx pattern will become more active during the long range fcst
period. A low pressure system and cold front will bring rain and a
chance of thunderstorms Wednesday night and Thursday.

Timing of the cold front through our fcst area is still uncertain
and potential for any severe wx with this system will be largely
contingent on how much instability will develop prior to fropa. It
seems that overall medium range guidance trends favor a slightly
slower solution such that fropa would likely not occur until
Thursday afternoon or evening.

Dry weather will briefly return Thursday night into Friday before
another system brings more rain and potential for convection Friday
night through the weekend. Some of the rainfall through the weekend
could be heavy as the system will have ample gulf moisture to work
with. Temperatures should average fairly close to normal for this
time of year through the long range fcst period.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 135 PM EDT Mon Apr 24 2017

VFR weather is expected to prevail into the night. Though some
patchy fog is possible late tonight, MVFR conditions may come
about due to lowering ceilings instead of visibilities. IFR levels
are not expected.

&&

.MARINE...
Issued at 1029 AM EDT Mon Apr 24 2017

I used the HRRR to update the wind speed and direction for the
rest of today with the hope of better capturing the lake breeze
circulation. This turns the wind to the west by late morning or
early afternoon across the near shore waters. The NAMNest does not
do that but keeps it Southeast. Given the temperature rises to
nearly 30 degrees over the land, higher than the Lake Michigan
Water temperature and gradient winds are not all that strong, it
would seem to me the HRRR, RAP model have a better forecast.

&&

.HYDROLOGY...
Issued at 126 PM EDT Mon Apr 24 2017

Most river streamflow rates are running between the 75th and 85th
percentiles for April 24, so they are still running above normal
despite most having fallen below bankfull. An active weather pattern
will return late Wednesday and continue into next week. The concern
for rebounding river levels and possible flooding remains,
especially after the rain event likely to occur between Saturday to
Monday. A majority of the latest GFS and ECMWF ensemble members
produce at least 2 inches of rainfall over the area by next
Monday.

&&

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

&&

$$

UPDATE...WDM
SYNOPSIS...MJS
SHORT TERM...Ostuno
LONG TERM...Laurens
AVIATION...63
HYDROLOGY...CAS
MARINE...WDM



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