Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 301136
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
736 AM EDT Thu Mar 30 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 323 AM EDT Thu Mar 30 2017

Wet conditions are expected through Friday evening with a chance for
thunderstorms today and early tonight mainly south of I-96. After a
dry Saturday, the next period of rain begins Sunday and lasts into
the beginning of the coming work week. After seasonably cool
temperatures today and Friday, temperatures this weekend and much of
the coming week will be near or above normal with highs in the
50s.

&&

.UPDATE...
Issued at 449 AM EDT Thu Mar 30 2017

After discussion with Gaylord office, have bumped up snow amounts
slightly over northern Clare and Osceola counties where a strong
fgen band continues just north of US-10 in a region with a marginally
favorable wet bulb zero profile. This is a very sensitive tipping
point type of scenario in which there could be enough local
diabatic cooling beneath the band to change precip over to snow
with a quick accumulation. Or on the other hand, temperatures
will remain warm enough to curtail accumulations. The area in
question is sparsely populated, but we did obtain a report of
little or no snow falling around Luther beneath the band that has
been sampled fairly well by the KAPX radar. Again, we may still
end up with little or no accumulations in Clare and Osceola
Counties, but this certainly has gotten our attention.

&&

.SHORT TERM...(Today through Saturday)
Issued at 323 AM EDT Thu Mar 30 2017

Have scaled back snow accumulations slightly based on warmer
temperatures. Main area of concern for snow continues to be
northeast zones where surface dewpoints in the low to mid 20s
combined with mid 30s temps will likely keep wet bulb zero height
low enough for accumulations. Also, radar continues to show an
fgen band extending eastward across the US-10 corridor, so there
certainly remains potential for accumulations into mid morning
with localized moderate to briefly heavy precipitation.

SREF and particularly deterministic runs like the RAP spread
sufficient instability / MUCAPE > 250 J per kg / into the
forecastareawide area that has correlated well with lightning
upstream. Will closely follow the SPC Day1 general thunder outlook
area for delineation. Discussed with IWX and agree that thunder
threat could linger after dark to the east.

Otherwise, good agreement on precipitation exiting the area Friday
evening.

.LONG TERM...(Saturday night through Wednesday)
Issued at 323 AM EDT Thu Mar 30 2017

Split flow will continue through the period and will feature the
type of weather we`ve been experiencing for the last several days.

High pressure over the Great Lakes Saturday night will move east as
low pressure over the Southern Plains moves northeast. The northern
stream trough will move across southern Ontario as the southern
stream counterpart moves across the Arklatex. There will be some
phasing Sunday over the Ohio Valley and so we can expect some light
rain. These systems have been taking a day and a half or so to move
through and so wet weather is anticipated from Sunday afternoon
through Monday night. After that a day or so of dry weather with
short wave ridging moving over the state followed by another Plains
low moving toward the Great Lakes. This system would affect the cwa
Wednesday or so and appears on models a bit deeper than the system
currently moving through the cwa. So that will likely result in a
bit warmer air being pulled north into Lower Michigan Wednesday. We
don`t have thunder in the grids yet, but wouldn`t be surprised to
see it eventually.

Highs will be mostly in the 50s through the period.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 736 AM EDT Thu Mar 30 2017

Expect a gradual lowering of ceilings areawide to below IFR
thresholds by afternoon with a high probability of LIFR ceilings
areawide after 00Z. Thunder would be most likely at the AZO and
BTL terminals before 15Z and then again at AZO, BTL, and JXN
terminals after 18Z, with lesser probabilities farther north at
GRR and LAN. Thunder threat should end from west to east this
evening.

&&

.MARINE...
Issued at 323 AM EDT Thu Mar 30 2017

Made minor tweaks to extend southern SCA headline times based on
latest WW3 guidance. Strong offshore component to flow will limit
wave growth today, but expect 3 to 5 footers to be more common by
evening.


&&

.HYDROLOGY...
Issued at 1158 AM EDT Wed Mar 29 2017

Widespread precipitation is expected across West Michigan from
late tonight through Friday. Basin average amounts of three
quarters of an inch to an inch can be expected. Area rivers levels
are currently elevated from the previous rainfall event...with
advisories in place for Ionia, Hastings, and Holt. While most local
rivers should experience falling stages through tonight...the
precipitation over the next 36 hours will create a new round of
rises to develop. Current advisory products attempt to illustrate
this scenario.

Some of the 12Z model output suggests heavier precipitation than
currently included as input to the river models. These higher
amounts...if they materialize... could produce above bankfull
rises on many more rivers and streams across West Michigan. Those
with interests on area rivers should closely monitor the
situation.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory until 11 PM EDT Friday for LMZ848-849.

     Small Craft Advisory until 4 AM EDT Friday for LMZ844>847.

&&

$$

UPDATE...TJT
SYNOPSIS...TJT
SHORT TERM...TJT
LONG TERM...04
AVIATION...TJT
HYDROLOGY...MWS
MARINE...TJT



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