FXUS63 KAPX 060103

Area Forecast Discussion
National Weather Service Gaylord MI
903 PM EDT Wed May 5 2021

Issued at 903 PM EDT Wed May 5 2021

Narrow ridge of high pressure extends from the Texas thru the Mid
Mississippi Valley into Michigan this evening. Meanwhile...weak
area of low pressure is developing over Nebraska...generating
showers and thunderstorms ahead of the associated cold front.
Closer to home...loss of diurnal instability with sunset has
resulted in a quick diminish in sct/bkn CU across portions of our
CWA. However...clearing skies this evening will give way to
increasing mid and high clouds from the west in advance of the
upstream low. This system will slide E/SE thru the Southern Great
Lakes over the next 24 hours...resulting in increasing clouds
tonight and increasing chances of showers on Thursday. Still
appears any shower chances will hold off until after sunrise
tomorrow. Period of clearing skies tonight combined with
diminishing wind speeds and a rather cold airmass still in place
across the Great Lakes will lead to overnight lows in the low to
mid 30s and the development of widespread frost overnight. Will
certainly maintain all Frost Advisory headlines in effect for most
of Northern Lower Michigan thru the remainder of the night.


.NEAR TERM...(Through Tonight)
Issued at 349 PM EDT Wed May 5 2021

...Chilly temperatures continue...

High impact weather potential: Frost concerns continue tonight for
parts of the area.

Pattern synopsis and forecast:

Amplified upper level pattern found across NOAM early this
afternoon, consisting of sharp ridge axis running up the west coast
and downstream troughing extending from Hudson Bay south into the
northern Gulf Coast states. Northern Michigan fully under the
influence of the latter, with deep northwest flow resulting in
temperatures running several degrees below normal. Increased mixing
and arrival of some dry air is finally helping scour out some of the
persistent overcast (definitely a fall-like look and feel to the
weather this morning). Well defined shortwave and attendant much
weaker surface reflection digging southeast across the northern
Plains, producing areas of mostly light showers as it does so.
Surface ridge axis out ahead of this feature building into the
western Great Lakes.

Area will remain centered under overhead troughing for the next
several days as long-wave movement slows to a crawl. Upstream
shortwave remains progressive, digging into the northern Ohio Valley
as we head through Thursday. Weak surface high continues to build
east, centering directly overhead this evening.

Primary forecast concerns/challenges:

Main focus centers on temperatures trends and attendant headline


Per the usual, another challenging temperature forecast
tonight...predicated completely on cloud and winds speed trends.
Addressing the latter first...given building of surface high, gotta
believe winds go light to even calm tonight. A bit more challenging
cloud forecast as what should be mainly clear to partly cloudy skies
this evening gives way to increasing mid and higher level clouds
overnight as that upstream wave digs southeast. May even see just
deep enough moisture to wring out a few sprinkles down near Manistee
late tonight. Gotta believe temperatures will spiral downward fairly
quickly just after sunset, perhaps stabilizing a bit as clouds
increase late tonight. Again, statistical guidance appears a bit too
cold, showing some interior areas dipping into the 20s. Don`t think
it gets that cold, but could still see some widespread readings in
the lower and middle 30s across most of the area. Will expand
inherited frost advisory a bit further south, once again making the
assumption that skies clear long enough for temperatures to fall
quickly this evening.


.SHORT TERM...(Thursday through Saturday)
Issued at 349 PM EDT Wed May 5 2021

High Impact Weather Potential: Precip chances, potential
frost/freeze issues at night.

Pattern Synopsis:

A closed upper-level low will be centered over James Bay through the
end of the week as embedded shortwaves pivot through the main flow
over the Great Lakes. The first shortwave looks to move overhead
Thursday morning as a second, more compact shortwave is expected to
progress into the area Friday morning. This may result in relatively
weak surface pressure falls amidst much broader surface high
pressure expanding across the northern Great Plains/Midwest.


Mainly light precip chances are expected across northern Michigan
both Thursday and Friday as these aforementioned shortwaves move
overhead. While the best chances for rain will lie south of the CWA
Thursday collocated with more favorable forcing, the northern end of
this precip is expected to move across northern lower through the
day. Some increased chances of heavier downpours may come across
areas near Lake Huron where a lake breeze may push inland in the
presence of weak ambient winds, providing a strip of enhanced near-
surface convergence in an environment with non-zero instability
despite cool surface temps. However, some of this precip on Thursday
may struggle to reach the ground with relatively high low-level T-Td
spreads during the day.

A better chance for precip across northern lower may be in store for
us Friday morning as better forcing aloft slides into the Great
Lakes. As noted in the synopsis, guidance hints at surface pressure
falls/meso-low development - which is certainly believable
considering the shortwave moving overhead combined with weak
background flow. This may bring some enhanced precip chances to the
area, mainly south of the bridge. With cooler temps near freezing
moving in Thursday night, slushy flakes may mix in Friday morning
across some areas.

The main impacts across northern Michigan during the short term,
however, may come in the form of cold temperatures overnight.
Frost/freeze concerns will rise once again Thursday night and Friday
night. While overnight lows are expected to be near freezing
Thursday night, frost/freeze potential may be somewhat mitigated by
cloud cover/precip moving in. The better chance appears to be Friday
night as clear skies are expected overnight. While winds will be
light, speeds of around 5 mph may keep the near-surface layer mixed
enough so temps don`t drop comfortably into the mid/upper 20s.
Temperatures near or slightly below freezing are anticipated for
some areas, especially interior northern Michigan, While other areas
remain in the mid-30s. Frost/freeze potential during these upcoming
nights will continue to be monitored closely.

.LONG TERM...(Saturday night through Wednesday)
Issued at 349 PM EDT Wed May 5 2021

High Impact Weather Potential: Continued monitoring of frost/freeze

Amplified troughing associated with a closed upper-level low
centered over James Bay will gradually pivot east over the weekend
into early next week, centering the Great Lakes on the backside of
this flow ahead of approaching ridging from the west. Subsidence
provided aloft should help build surface high pressure across most
of the central CONUS by early next week, keeping precipitation
chances low across the state. With no substantial southerly
advections of a warmer airmass into the Great Lakes, temperatures
are expected to remain solidly below normal for the beginning of
May. Highs near 50 are expected across northern Michigan through the
weekend, which would be over 10 degrees below normal for the time of
year. As has been the story as of late, frost/freeze potential will
continue to be a concern overnight into early next week as these
chilly temps stick around.


.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 703 PM EDT Wed May 5 2021

Low pressure centered over the Dakotas will drop SE thru the
Southern Great Lakes tonight into Thursday...resulting in an
increase in clouds and chances of rain showers on Thursday.
Overall conditions will remain VFR thru the 24 hours TAF forecast
period despite increasing chances of rain. Surface winds will
remain from the W/NW AOB 10 kts thru Thursday.


Issued at 349 PM EDT Wed May 5 2021

Gusty northwest winds will quickly subside this evening as high
pressure builds overhead. Current trends support both winds and
waves remaining below advisory levels through at least Thursday


MI...FROST ADVISORY from midnight tonight to 9 AM EDT Thursday for



NWS APX Office Area Forecast Discussion