Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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362
FXUS63 KDTX 220410
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1110 PM EST Wed Feb 21 2018


.AVIATION...

Surface anticyclone building across the northern Great Lakes will
allow low level flow trajectories to become increasingly more
easterly tonight. Lower level dry air advection will continue to
dissipate lower boundary layer/MVFR cloud overnight, also getting
additional support with thickening mid cloud aloft. Long period of
VFR conditions right into tomorrow for most of the TAF sites. Will
be watching for potential of light precipitation to lift northward
across the Ohio border, into Michigan between 10-14Z. HRRR and
Regional GEM are the most bullish bringing light precipitation just
south of DTW, while the NAM is much farther south. Looking through
thermal fields suggests that any forcing that could bring
precipitation will be very high in column upwards of 10-12kft agl, as
low level dry air feed will hold strong. Preference is to continue a
dry forecast with virga likely overspreading the terminal. It
appears that for precipitation to occur its going to take a greater
northward displacement than the consensus. Also, high confidence that
precipitation type will be snow due to wet bulbing effects. To
reiterate, a dry forecast will be in the Detroit TAFs.

/DTW THRESHOLD PROBABILITIES...

* High for ceiling 5000 feet or less right at start of the TAF
  period. Low tonight.

&&

.PREV DISCUSSION...
Issued at 330 PM EST Wed Feb 21 2018

DISCUSSION...

Flood watch will be allowed to expire.

Slow weakening/flattening of the summer-like upper level ridge (595
DAM at 500 MB) anchored just off the East Coast over the next
several days.

Frontal boundary and record setting moisture axis has pushed into
the southern Ohio Valley, with drier and colder air filtering into
southern Lower Michigan this evening, as surface dew pts lower into
the 20s and upper teens. Even with mid/high clouds around tonight,
temperatures should have no problem falling into the 20s, leading to
any residual standing water freezing up. Motorists should be
cognizant of the potential icy patches on area roads, not
to mention additional potholes.

Upper wave coming out of Texas this afternoon will track through
lower Michigan tomorrow morning. The question is whether low level
dry air and anticylonic flow will hold on to maintain dry
conditions, with locations toward the Ohio border possibly getting
clipped. 12z Regional Gem remains most adamant, while NAM/GFS hold
serve and suppress activity just to the south. Will carry chance
pops south of Eight Mile, as latest RAP/HRRR showing a real close
call. Thermal profiles suggesting it would be just cold enough for
snow, as you have to get up toward 600 MB for ice nuclei present.

Yet another upper wave coming out of Texas on Thursday. Stronger and
deeper southwest flow with this one will allow deeper moisture to
make better inroads north, as PW values around 1 inch reach the
southern Michigan border by 12z Friday. The strong high pressure
over Eastern Canada will be giving way, but there still an
opportunity for surface temps to be at or below freezing as the
precipitation initially develops, especially if it occurs before
sunrise Friday. Good surge of warm advection then taking over
during the day on Friday, with 925/850 mb temps rising into the mid
single numbers.

Low pressure developing in conjunction with a shortwave ejecting
from the Western US trough will bring another chance for widespread
precipitation to the region this weekend. Model guidance is in
fairly good agreement that this low will track from the Central
Plains on Saturday to the UP of Michigan by early Sunday. A
rain/snow mix will be possible with the onset of precipitation on
Saturday before strengthening southerly flow pulls warm air
northward and transitions precipitation to rain. Precipitation then
ends early Sunday as a cold front sweeps through the region. Behind
the front, better mixing and a tightening pressure gradient courtesy
of the strong low pressure system will bring gusty winds Sunday
afternoon as highs reach the upper 40s.

High pressure builds across the region early next week bringing dry,
quiet conditions as upper level ridging re-establishes itself over
the Eastern US. Temperatures look to remain above average through
Tuesday with highs in the lower to mid 40s and lows in the upper 20s
to lower 30s.

MARINE...

A broad region of high pressure will move across the northern Great
Lakes tonight through Thursday. This will maintain dry conditions
over all marine areas except possibly some light snow over western
Lake Erie. The high will also maintain light wind across the north
half of Lake Huron and northeast wind mainly less than 20 knots over
southern marine areas. Wind will then veer to the south by Friday as
the next low pressure system moves into the western Great Lakes.
This system will bring generous coverage of mixed precipitation
changing to rain. Mild air will then be swept out by the associated
cold front on moderate wind speed shifting to northwest Friday
night. High pressure moves in briefly Saturday before a stronger low
pressure system arrives during Sunday.

HYDROLOGY...

Rain has ended across southeast Michigan after a two day stretch
that produced 2 to 3 inches over a broad area of the region. The
Flood Watch has been cancelled for the potential of areal flooding,
however run-off from the rain and melted snow will continue to feed
creeks, streams, and rivers. Flood warnings are in effect for most
of the primary river basins around southeast Michigan and will
likely remain in effect through the end of the week. Additional
mixed precipitation and rain during Friday is not expected to
contribute to additional flooding or prolong existing flooding.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&

$$

AVIATION.....CB
DISCUSSION...SF/JD
MARINE.......BT
HYDROLOGY....BT


You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.



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