470
FXUS63 KMQT 141620
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
1220 PM EDT Wed Aug 14 2024

.KEY MESSAGES...

- Light rain showers possible over the north central this
  afternoon via the lake breeze.

- Wet period with showers and some thunderstorms developing
  Thursday, continuing Friday, then ending west to east on
  Saturday.

&&

.SHORT TERM /THROUGH THIS AFTERNOON/...
Issued at 225 AM EDT Wed Aug 14 2024

High pressure continues to hang over the region today, keeping skies
mostly clear into this evening. That being said, webcams,
observations, and satellite imagery show some thin patches of fog
developing across the Upper Peninsula early this morning, reducing
visibilities here and there. While dense fog is not expected this
morning, be alert for wildlife and other vehicles when going through
the fog patches. Current observations have the temperatures in the
mid 50s to mid 60s across the area; I`m thinking that the
temperatures will lower a few more degrees before the sun rises.
Once the sun rises, expect any fog to quickly dissipate.

Moving into the daylight hours, expect a near rinse-and-repeat of
yesterday. However, with more stable air in the mid levels expected
today, convection will have a harder time getting fired-up this
afternoon in comparison to yesterday. Therefore, while there is a
small (20 percent or less) chance of seeing some lake-breeze induced
rain showers this afternoon (mainly over the north central), I think
CIN in the mid-levels will prevent any convection from achieving
glaciation (i.e. the updrafts will not get high enough in the
atmosphere for thunderstorms). Otherwise, expect temperatures and
winds to be about the same as what they were yesterday, save for the
Lake Michigan lake breeze going further inland in comparison to the
Lake Superior lake breeze.

&&

.LONG TERM /TONIGHT THROUGH TUESDAY/...
Issued at 435 AM EDT Wed Aug 14 2024

Medium range model guidance is in good agreement on the large scale
flow evolution over N America thru the weekend. As a group of
shortwaves currently over the Pacific NW and Alberta/Saskatchewan
progress eastward, mid-level ridging will modestly build northward
into Saskatchewan/Manitoba Thu/Fri. In response, the shortwaves will
consolidate into a modestly amplifying trof into the Great Lakes
region Fri/Sat. Early next week, ridging will more sharply amplify
from NM/TX northward thru central Canada with positive mid-level
height anomalies maximizing to the w and nw of Hudson Bay. This will
force the trof moving thru the Great Lakes region to gain amplitude
over eastern N America early next week. Although there is
disagreement on the amplitude/structure of the mid-level ridging
thru central N America early next week, some degree of nw flow will
be favored into the Upper Lakes. For Upper MI, this evolution of the
flow with troffing developing thru the Great Lakes region will bring
shra to the area Thu thru Sat. While all day rain is not expected,
potential is high for all of Upper MI to see at least light to mdt
rainfall over the course of the 3 days. Ensemble guidance suggests a
20-60pct probability of rainfall amounts of an inch or more by
Saturday evening, highest probability w to s central. The rainfall
is needed as the pattern has turned drier over the last few weeks. A
large portion of Upper MI is currently running at 25-70pct of normal
rainfall over the last 30 days with the largest area under 50pct
over the w half of Upper MI. After a return to dry weather on Sun,
there is uncertainty early next week on progression of shortwaves
around the ridge or even thru it. Summertime NW flow can be
notorious for producing diurnal convection with even the subtlest of
shortwaves, so would not be surprised to see isold shra/tsra any day
from Mon-Wed. Greater coverage of shra/tsra will occur if a more
defined wave passes.

Beginning tonight, in response to the trof/shortwaves moving across
the Northern Plains, shra will advance toward Upper MI under a good
surge of isentropic ascent and 850-700mb moisture transport. Opted
for a middle of the road approach for timing, bringing shra
potential into far w to s central Upper MI toward 12z Thu. Often
slower is the way to go, and it is noted that some models hold off
pcpn from crossing the WI/MI stateline until late Thu morning. Would
not be surprised at all if later fcsts need to push back pcpn
timing.

During Thu/Thu night, modestly amplifying mid-level trof will move
to the Upper Mississippi Valley with sfc low pres developing into
northern WI. Surge of isentropic ascent and 850-700mb moisture
transport ahead of the trof will spread an initial band of shra
across the fcst area on Thu. Instability is very limited initially,
so don`t anticipate much, if any, thunder with the leading band of
shra. After the initial band of shra, shra coverage will be more on
the sct/nmrs side. Models still show precipitable water increasing
to 150-170pct of normal along with warm cloud depths increasing to
around 12kft to increase warm rain processes. That will support the
potential of locally hvy downpours.

Sct/nmrs shra and some tsra will continue on Fri as
troffing/potential weakly closed off mid-level low drift over the
western Great Lakes while associated sfc low slowly moves e across
northern WI or Upper MI. With ocnl shra and abundant cloud cover,
high temps should be held to mostly the upper 60s/lwr 70s F. Any
breaks in the cloud cover will boost instability, supporting an
increase in thunder. However, with deep layer shear under 20kt (even
under 10kt across much of the area), environment will not support
organized storms and svr risk, even with any building of instability
during the day. Hvy downpours would be likely with any tsra.

Models diverge on how quickly the mid-level trof shifts e on Sat,
and that affects pcpn fcst. Consensus of recent model runs, not just
the 00z model runs, suggests some shra will continue on Sat, but
diminishing/ending w to e. If faster solutions work out, Sat would
be a dry day, at least across western Upper MI.

Dry weather is then expected on Sun as trof continues shifting e of
the area. As previously mentioned, Upper MI will remain under some
degree of NW flow early next week, and during summertime, NW flow
can result in isold convection with even the subtlest of shortwaves.
Last day or so of medium range model runs have suggested that a more
defined wave may arrive Tue or Wed, offering a better potential of
something more than isold shra/tsra. Until models move toward some
consistency, pcpn chc remains low in the 20-30pct range.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1219 PM EDT Wed Aug 14 2024

VFR conditions dominate through tonight as high pressure ridging
slowly gives way to an incoming shortwave low currently over the
Northern Plains. Rain will move into IWD towards the end of the
forecast period with conditions dropping to MVFR.

&&

.MARINE...
Issued at 435 AM EDT Wed Aug 14 2024

With sfc high pres that provided light winds in recent days shifting
e, winds will increase slightly, but still remain under 20kt
today/tonight. During Thu/Fri, low pres will develop e and ne into
WI/Upper MI, bringing increasing easterly winds to Lake Superior.
Expect winds to gust up to around 25kt, particularly Thu aftn thru
much of Thu night. Exact track of the sfc low will determine whether
these stronger wind gusts continue on Fri, but it does appear that
pres gradient will overall relax some, so winds should settle back a
bit across much of the lake on Fri, especially across eastern Lake
Superior which will be closer to the low pres center. As the low
departs, a period of n to nw winds gusting to 20-25kt is possible
Fri night into Sat, mainly across the e half of Lake Superior.
Expect winds under 20kt on Sun as high pres ridging builds to Lake
Superior.

&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.

&&

$$

SHORT TERM...TAP
LONG TERM...Rolfson
AVIATION...07
MARINE...Rolfson