257
FXUS63 KMQT 170724
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
324 AM EDT Tue Sep 17 2024

.KEY MESSAGES...

- Extended stretch of well above normal temperatures continues through
  at least Saturday with highs mainly in the upper 70s and 80s.

- Next credible chances of precipitation arrive Friday into the
  weekend.

&&

.SHORT TERM /THROUGH THIS AFTERNOON/...
Issued at 323 AM EDT Tue Sep 17 2024

Water vapor imagery and RAP analysis show mid-level troffing over
the western U.S. Downstream, sw flow prevails thru the Upper
Mississippi Valley into se Canada overtop ridging over the ne U.S.
Within this flow, a couple of shortwaves are supporting clusters of
shra/tsra from the ND/Manitoba border eastward along the Ontario/MN
border region. Closer to home, conditions across Upper MI early this
morning are nearly a carbon copy of 24hrs ago. Stirring southerly
winds in the downslope areas near Lake Superior from western to n
central Upper MI are resulting in another incredibly warm early
morning for mid Sept. Temps as of 07z are in the upper 60s and lwr
70s F in that area, above the normal high temps at this time of
year. Same as yesterday morning, Big Bay is the warm spot. At 75F,
the temp there is 1 degree lower than 24hrs ago. Across s central
and eastern Upper MI, winds are decoupled, and with mostly clear
skies, temps have fallen to the low and mid 50s F at many locations.
Patchy, shallow fog is forming again in that area as well. The
patchy fog will burn off an hr or so after sunrise.

With shortwaves supporting the aforementioned shra/tsra heading ene,
don`t expect any pcpn for Upper MI today. Mid morning 850mb temps
today are indicated to be about 1C lower than yesterday morning, and
this should, in general, translate to highs today being a couple of
degrees lower than yesterday. So, expect another unseasonably warm
day for mid Sept with highs ranging thru the 80s F with a few spots
into the upper 80s F under mainly sunny skies. Southerly winds will
hold temps to the 70s F along Lake MI. Record high of 82F here at
the NWS office location is very likely to be broken. Low-level air
mass today is just a bit drier than yesterday as noted by 850mb dwpt
depressions, and this will result in sfc dwpts mixing out a bit lwr
than yesterday as well. More areas across the central and e not
immediately downstream of the southerly flow off of Lake MI should
see dwpts fall thru the 50s with low end near 50F. This will bring
RH down into the 30s with low end nearing 30 pct. Fortunately, wind
gusts will only be in the 10-15mph this aftn. Still, the lengthening
dry spell is becoming an ever greater concern for wildfire
potential. Over the last 2 weeks, pcpn has been been less than 50
pct of normal across all but nw Upper MI with large areas at less
than 25 pct of normal.

&&

.LONG TERM /TUESDAY THROUGH MONDAY/...
Issued at 319 PM EDT Mon Sep 16 2024

Through the work week, the pattern aloft remains very blocky with a
closed low over the US Southeast through Thursday night. The rex-
block ridge that`s been residing north of the closed low lately will
be replaced by another ridge that will be causing 500mb height
anomalies over northern Ontario to climb to near +30 dam. By Friday,
the low wave number blocked pattern will shift to a high
wavenumber active pattern as the closed low shifts northeast
from under the second ridge, resulting in troughs over the
Eastern Seaboard, the Northern Plains, and over the Desert
Southwest with ridges in between each trough. The surface
weather will reflect this pattern change as the previous dry
conditions and anomalous warmth will be replaced by more
widespread chances of rain into next weekend along with more
seasonable temperatures.

Tuesday looks to be a dry day as the most influential surface
feature remains a 1025mb high centered over New York during the
morning. Global deterministic models show a shortwave passing
through northern Ontario through the day and two of the members of
the HREF (NSSL WRF and FV3 WRF) show precipitation over Isle Royale
and western Lake Superior in response to surface troughing draped
south of the shortwave. Therefore, this forecast will add some
chance (15-26%) PoPs for those areas overnight. With HREF mean
MUCAPE of up to 750 J/kg, an isolated thunderstorm cannot be ruled
out, but severe weather is not expected as shear values of below 20
kt will not allow for updrafts to be organized in a meaningful
fashion.

Despite the erosion of the first ridge aloft over the Great Lakes,
it will be immediately replaced by another ridge moving over from
the Great Plains, resulting in Wednesday and Thursday being another
pair of dry days. Minimum RH values during those days do remain
above critical thresholds, but with wide swaths of the UP going
a full week without rain and nearly all of the UP having less
than a quarter inch of precip over the last week, drying fuels
may be a concern to some fire partners. Thankfully, under the
ridging aloft and with a lack of nearby low pressure centers,
winds remain light, alleviating some of those fire weather
concerns. A few record highs and record warm lows may be under
threat as the NAEFS highlights the near-surface temperatures
above the 90th percentile of its climatology. Lighter winds and
mainly clear skies will provide good setups for radiation fog
each overnight, especially in the south- central, where the Euro
visibility meteograms highlight 20% chances for dense fog.
Leaving just patchy fog in the grids for now until confidence
increases.

As the blocking pattern shifts quickly into a quite active pattern,
troughing will finally arrive from the west late Thursday into
Friday, allowing for higher PoPs to arrive with widespread wetting
rain being likely by the end of the weekend. Model spread is still
high in the details (which is understandable given the increased
number of features to track over the CONUS for next weekend), but
the LREF highlights the western half of the UP as at least
33-66% likely to reach a half inch of rain by the end of the
weekend with the east half with similar probabilities to reach a
quarter inch. NBM high temperatures will also cool behind the
trough with highs closer to normal for this time of year in the
upper 60s and lower 70s.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 126 AM EDT Tue Sep 17 2024

VFR conditions should prevail through the TAF period. Patchy shallow
fog cannot totally be ruled out at SAW in the 08-12Z timeframe, but
probability of MVFR or lower is less than 20%. Southerly winds may
gust to around 20 kt at times at IWD/SAW this afternoon.

&&

.MARINE...
Issued at 319 PM EDT Mon Sep 16 2024

Light winds of 20 knots or less continue over Lake Superior this
week as high pressure ridging over the eastern U.S. influences our
weather pattern for the next several days. Nevertheless, some
showers and thunderstorms are possible tonight and again Tuesday
night as shortwave lows ride along the ridging overtop the Upper
Great Lakes. Chances for 20 kt gusts increase Friday into the
weekend as troughing finally arrives from the west, though details
on the exact track of the surface features are uncertain and will
have a large influence on the details of gusty conditions.

&&

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

&&

$$

SHORT TERM...Rolfson
LONG TERM...GS
AVIATION...Thompson
MARINE...GS