FXUS63 KGRR 292312

Area Forecast Discussion
National Weather Service Grand Rapids MI
712 PM EDT Mon May 29 2023


.SHORT TERM...(This evening through Tuesday night)
Issued at 308 PM EDT Mon May 29 2023

The upper-air pattern continues to be characterized by a Rex block
over eastern North America, comprised of an upper high over the
Great Lakes an upper low over the southeast CONUS, with fairly weak
tropospheric flow over the region. At the surface, a broad synoptic
ridge is draped over the region -- extending from a high over
eastern Canada -- with a weak/diffuse surface low over the mid
Atlantic coast. This regime is maintaining weak low-level easterly
flow on a broad scale, but a mesoscale lake-breeze circulation has
developed again this afternoon, similar to recent days.

A modest increase in southeasterly low-level flow (10-20 kts at 925
mb) tonight should facilitate weak low-level moisture transport into
the region. Short-range guidance suggests that surface dewpoints
should generally increase after daybreak Tue as the convective
boundary layer deepens and entrains this moisture, with mid 40s-mid
50s dewpoints likely to be common across the area during the
afternoon. The arrival of this low-level moisture -- with a
corresponding reduction in convective temps (likely into the mid 80s
F) -- should yield widespread cumulus development across inland
areas on Tue, given sufficient boundary-layer warming. High temps on
Tue will likely be warmer than today, reaching the upper 80s to
around 90 F across inland areas, given the expectation of warmer 850-
mb temps.

12z HREF guidance suggests that isolated showers may develop on Tue
afternoon along/east of the lake-breeze front, where cumulus may
become sufficiently deep. However, RAP forecast profiles indicate a
fairly deep and dry subcloud boundary layer, suggesting that
evaporation/virga will be substantial beneath any precip-producing
clouds. Will opt to maintain PoPs below 15 percent (threshold for
slight-chance showers) with this update, but will introduce a slight
chance of sprinkles away from the lakeshore.

.LONG TERM...(Wednesday through Monday)
Issued at 308 PM EDT Mon May 29 2023

Our focus in the long term portion of the forecast will be on
rain chances, albeit small ones, through much of the period from
Wednesday through Sunday, with some possible better chances for rain
coming next Monday. We will see a trend of warmer temperatures
through next weekend, and generally a slow increase in moisture. The
moisture trend is a bit complicated, and we will discuss further

Upper ridge will remain in control of the weather across the area
into early next weekend in one form or another. This will keep
widespread and appreciable rain out of the area likely into next

There are caveats to this thinking though as we will see the
potential for a few mainly diurnal showers and storms increase
slightly for Wednesday and Thursday. What happens is that we will
see a bit higher moisture move in with a southerly component to the
low level flow develop. This will bring in sfc dew points into the
50s, and maybe even 60s by Thursday. This moisture will combine with
a fairly stout lake breeze convergence band that is forecast by the
models to pop a few showers and storms in the afternoon. Convergence
is almost maximized with a synoptic flow from the SE, and a lake
breeze from the NW developing. So while most of the area will stay
dry, there could be some locally heavy downpours with slow moving
cells as the lake breeze moves further inland.

The rain chances might be stunted a bit for Friday and Saturday as
the flow becomes more easterly by then, and advects a pocket of much
drier air over the area. Temperatures will continue to warm at least
a couple of degrees per day with almost full sun and good mixing
taking place.

We are then looking at a pattern change poised to take place in one
way or another sometime next Sunday/Monday, with details to be
ironed out. The general sense is that some strong upper energy
across Canada will drop south and push a fairly potent backdoor cold
front south through the area on the front side of the large scale
ridge across the Plains.

The interesting part of this is that the last data shows an upper
low rotating toward the area from the NE, and a moisture feed off of
the Atlantic. However this happens is quite uncertain at this time.
There is a fairly decent signal in the Ensemble means that cooler
air will replace the heat toward next weekend and then the following
week. Rain chances will be quite uncertain depending on if the front
will have some moisture to tap as it moves through, but it will be a
better chance that strong ridging overhead.


.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 712 PM EDT Mon May 29 2023

VFR conditions to continue through Tuesday evening. There could be
some shallow ground fog at JXN but this should not affect flight
operations. Winds will be light and variable tonight and generally
from the southeast below 10 knots on Tuesday. Winds will go west
at MKG in the afternoon as the lake breeze moves through.


Issued at 308 PM EDT Mon May 29 2023

A broad ridge of high pressure remains situated over the region,
providing a fairly weak synoptic-scale surface pressure gradient.
Over the next several days, winds in nearshore waters will continue
to be primarily modulated by afternoon lake-breeze development and
nighttime land-breeze development--likely through at least Friday.
Winds speeds are expected to be light (15 kts of less), limiting
wave development in nearshore waters to 2 feet or less.


Issued at 308 PM EDT Mon May 29 2023

Fire danger only continues to increase with the continued dry
pattern, and will continue on that trend for the foreseeable future.
The biggest concern would be in the Jack Pine Forests across Central
Lower, but just about all inland areas have extreme fire danger as
of this afternoon.

Dew points are progged to come up gradually over the next few days
with a southerly wind advecting the slightly higher moisture over
the area. Temps will be warming too, and will likely keep RHs low.

We do not see all three criteria for Red Flag Warnings being met in
the next couple of days. If there is a sliver lining in things, the
winds will remain relatively light. If the land management agencies
see conditions bad enough without the wind, Red Flag Warnings may be
needed eventually.

This will continue until around Monday, June 5th when this pattern
is expected to break down, and cooler air will move in with some
better rain chances.


Issued at 308 PM EDT Mon May 29 2023

We looked up the records for the next week with the very warm to
hot conditions coming in. Many of these are quite high, and not
reachable, but there are a few here and there that could be in
jeopardy. Here are the records for the next couple of days. We
will likely send out social media messages with all of the data
for reference.

Record High Temps

            GRR       MKG       LAN       AZO       BTL       BIV
Tue 5/30  92-2019   90-2018   95-1895   94-1978   94-1895   94-1942
Wed 5/31  95-1934   88-2016   96-1895   93-1911   94-1919   92-1934
Thu 6/1   102-1934  88-2014   97-1934  102-1934  100-1934  100-1934

Record Warm Lows

            GRR       MKG       LAN       AZO       BTL       BIV
Tue 5/30  68-2018   74-2022   70-2022   72-2018   72-2018   70-2018
Wed 5/31  73-1937   70-1970   73-2022   71-2022   71-2022   73-1937
Thu 6/1   74-1934   66-1970   68-1970   71-1895   71-1895   75-1934





NWS GRR Office Area Forecast Discussion