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000
FXAK69 PAFG 201343
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
543 AM AKDT Tue Jul 20 2021

.SYNOPSIS...
A weather front along the West Coast of Alaska will move to the
Central Interior and Western North Slope tonight and then weaken
in place Wed into Thu. This will bringing significant rain to the
West Coast, Western North Slope and Western Interior today
through Wed, along with cooler temperatures. The rain will taper
off to scattered showers most areas by Wed.

Weak southerly chinook winds across the Alaska Range ahead of the
front are causing south winds 20 gusting to 40 mph through Alaska
Range Passes today. Most areas West of Nenana will keep RH above
30% today, but areas east of Nenana will have Min RH of 26-30%.
Near Delta Junction RH will drop to 26-30% and cause near Red
Flag Conditions from Donnelly Dome to Delta Junction for winds and
high temperatures today. The winds will start to decrease on Wed.

A thermal low pressure trough stretching from Howard Pass to
Tanana to Northway will move to Umiat to Northway today, then to
Old Crow to Beaver Creek, Yukon Territory, on Wed, and to Arctic
Village to Northway on Thu. Temperatures along this thermal trough
will be in the 80s across the Eastern Interior and inland North
Slope today, then fall into the 70s and low 80s on Wed and Thu as
the front advances and cools the area from the Central Interior
west. Temps will rebound a few degrees on Thu.

An unstable air mass near the thermal trough and east of the
weather front will cause isolated to widely scattered
thunderstorms today over much of the Interior and North Slope
East of Howard Pass to Farewell Lake, with thunderstorms starting
up in the late morning and continuing through midnight tonight. On
Wed expect isolated thunderstorms most areas east of Delta
Junction to Umiat with scattered thunderstorms along the ALCAN
Border Wed PM. This has lead to a Fire Weather Watch for lightning
east of Chalkyitsik and Northway on Wed PM. The strongest
instability remains east of the ALCAN Border on Wed. Will see
isolated thunderstorms on Thu east if Umiat and Tanana.

Aloft...
The long wave pattern consists of a strong ridge over Mainland
Alaska, a trough over the Eastern Gulf of Alaska, and a second
trough over the Chukchi Sea and the Bering Sea. Several strong
short wave troughs will move northeast out of the Bering Sea
trough and dig into the ridge over the next several days. This
will cause the ridge to move east over the Far Eastern Interior of
Alaska and NW Canada by Wed with the trough over the West Coast
of Alaska. This pattern will then hold in place through the
weekend. This means that hot and dry conditions over much of
Northern Alaska will see a wetting and cooling from the west
through Wed, with the Eastern Interior and Eastern North Slope
remaining warmer than normal through the weekend.


Surface....
A 1004 mb low 100 NM west of Point Hope will deepen to 998 mb by
4pm Tue, then persist in place through 4pm Wed, then slowly weaken
in place through 4pm Thu. A warm front that extends from this low
to Utqiagvik then northeast will persist into Wed then move
north. A cold front that extends south from this low to the Yukon
Delta will move east to Cape Lisburne to McGrath 4pm Tue, then to
Point Lay to Denali by 4am Wed, then to Utqiagvik to Denali bu 4pm
Wed, then weaken in place through Thu. Expect 0.25-1.00 inch of
rain along both fronts through Wed, with the heaviest amounts
along south facing slope. Expect NE winds 15-25kt along the Warm
front through tonight. Expect SW winds 5-15 kt along and west of
the cold front through tonight. East of the cold front, south
winds 20 mph gusting to 40 mph through Alaska Range Passes that
will continue into tonight and then decrease on Wed as the front
approaches. Temps will will be in the upper 70s and 80 east of
the cold front today, but drop into the 60s along and west of the
cold front. Smoke will advect north from fires today, then NE from
fires tonight and Wed.

A thermal low pressure trough stretching from Howard Pass to
Tanana to Northway will move to Umiat to Northway today, then to
Old Crow to Beaver Creek, Yukon Territory, on Wed, and to Arctic
Village to Northway on Thu. Temperatures along this thermal trough
will be in the 80s across the Eastern Interior and inland North
Slope today, then fall into the 70s and low 80s on Wed and Thu as
the front advances and cools the area from the Central Interior
west. Temps will rebound a few degrees on Thu.


&&

.DISCUSSION...
At 00Z, models initialize well aloft. Models show similar
solutions aloft and with precipitation through Thu. At the
surface at 06Z, models all verify well. Models show surface
solutions through Thu. Will use a blend of models through Thu for
all fields.

Coastal Hazard Potential Days 3 and 4...None.

&&

.FIRE WEATHER...
Weak southerly chinook winds across the Alaska Range ahead of the
front are causing south winds 20 gusting to 40 mph through Alaska
Range Passes today. Most areas West of Nenana will keep RH above
30% today, but areas east of Nenana will have Min RH of 26-30%.
Near Delta Junction RH will drop to 26-30% and cause near Red
Flag Conditions from Donnelly Dome to Delta Junction for winds and
high temperatures today. The winds will start to decrease on Wed.

A thermal low pressure trough stretching from Howard Pass to
Tanana to Northway will move to Umiat to Northway today, then to
Old Crow to Beaver Creek, Yukon Territory, on Wed, and to Arctic
Village to Northway on Thu. Temperatures along this thermal trough
will be in the 80s across the Eastern Interior and inland North
Slope today, then fall into the 70s and low 80s on Wed and Thu as
the front advances and cools the area from the Central Interior
west. Temps will rebound a few degrees on Thu.

An unstable air mass near the thermal trough and east of the
weather front will cause isolated to widely scattered
thunderstorms today over much of the Interior and North Slope
East of Howard Pass to Farewell Lake, with thunderstorms starting
up in the late morning and continuing through midnight tonight. On
Wed expect isolated thunderstorms most areas east of Delta
Junction to Umiat with scattered thunderstorms along the ALCAN
Border Wed PM. This has lead to a Fire Weather Watch for lightning
east of Chalkyitsik and Northway on Wed PM. The strongest
instability remains east of the ALCAN Border on Wed. Will see
isolated thunderstorms on Thu east if Umiat and Tanana.

&&

.HYDROLOGY...
Between 0.25 and 1.00 inch of rain is expected through Wed over
the West Coast, Western Interior and Western North Slope, with the
highest amounts along south facing slopes. This will cause rivers
in those areas to rise late this week, but no flooding is
expected. The Eastern Interior and North Slope could see minor small
stream flooding under thunderstorms today and Wed.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
Fire Weather Watch for AKZ220-AKZ224.

Small Craft Advisory for PKZ225-PKZ230.

Brisk Wind Advisory for PKZ235.
&&

$$

JB JUL 21