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000
FXAK69 PAFG 212214
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
214 PM AKDT Wed Jul 21 2021

.SYNOPSIS...
The pattern of West Coast troughiness and Interior ridging will
continue into the weekend. Isolated to scattered showers will
linger across the western Interior through Thursday as a front
washes out. Thunderstorm activity shifts to the eastern and
central Interior today through Friday. Along the AlCan border
scattered thunderstorms with the potential for frequent lightning,
heavy downpours, gusty winds, and small hail are expected today
and Thursday. Attention shifts to the southeast Interior Thursday
night and Friday, as an easterly wave brings the potential for
heavy rainfall.

&&

.DISCUSSION...
Upper Levels and Analysis...
Aloft, at 500 mb a long-wave trough remains draped south across the
Chukchi and Bering seas, extending eastward across the western
half of the mainland, with a strong shortwave moving across
Bristol Bay. As the shortwave moves east into the Gulf of Alaska
Thursday, ridging will rebuild across the Interior. The overall
pattern of troughing across the West Coast and ridging across the
Interior will persist into the weekend.

Models...
12Z model solutions in good agreement with the overall upper level
pattern and feature placement through Friday. By Friday night,
differences arise in the timing, placement, and strength of a
shortwave traversing the western Brooks Range and the northwest
Arctic Coast. The NAM is the fastest of all solutions, lifting the
shortwave north of Utqiagvik by mid-morning Saturday. The GFS is
the weakest and keeps the shortwave offshore, while the ECMWF and
Canadian track the feature across the coast, albeit slower than
the NAM. At the surface, model solutions too are similar for most
of the short term period. The largest differences become apparent
Friday with the precipitation associated with the easterly wave
moving across the southeast Interior. There are significant
differences in placement and amounts of QPF with the easterly
wave, as such, we have opted to go with a general blend to cover
location and amounts.

North Slope and Brooks Range... A surface low north of the
Chukotsk Peninsula will remain in place and weaken through
Thursday, lifting northeast on Friday. A weakening front extends
east from the low and north of the Arctic Coast. Another front
extends from Wainwright southeast into the Interior with precip
accompanying it. This front will weaken into Thursday. Isolated
thunderstorms expected this afternoon from Umiat east to the AlCan
border. Thunderstorm activity will spread westward Thursday
stretching into the western Brooks Range. Along the coast, onshore
flow will continue to support areas of stratus and fog.
Temperatures continue to trend downwards through Friday.

West Coast and Western Interior...
Weak impulses in the upper level flow, as well as a weakening
front across the central Interior will support isolated to
scattered showers lingering into Thursday. Drier conditions
expected on Friday. High temperatures will range from the upper
40s along the coast to the mid 60s inland. Temperatures climb a
few degrees across the western Interior on Friday.

Central and Eastern Interior...
Isolated to scattered showers occurring along and east of a front
stretching north from Denali to Wainwright will diminish this
afternoon and evening as the front weakens in place. Isolated
thunderstorms are expected to develop east of a line from
Fairbanks to Atigun Pass with scattered thunderstorms expected
along the AlCan border east of Chalkyitsik to Chicken. Models
continue to indicate strong instability along and east of the
AlCan border this afternoon and evening, though the strongest
instability stays east of the border. Some of these thunderstorms
could be strong and produce heavy downpours, frequent lightning,
gusty winds, and small hail. On Thursday and Friday most of the
Interior has the potential for isolated thunderstorms, with
scattered thunderstorms possible along the AlCan border once again
Thursday. An easterly wave moving over the SE Interior Thursday
night into Friday will bring the potential for heavy rainfall.
Half an inch to an inch and a half of rainfall accumulation is
possible during this period, with the highest amounts falling in
the Alaska Range. There remains differences in placement and
amounts, so confidence in rainfall totals is on the lower side at
this time. After a brief cool down in temperatures today,
temperatures will nudge upwards Thursday and Friday, with highs in
the 70s and 80s.

Extended Period Forecast Days 4 to 7...Little change in the
extended forecast as troughing out west battles ridging in the
Interior. A shortwave moving across the western Brooks Range and
the northwest Arctic Coast Saturday will bring another round of
precip Across the southeast Interior the potential for heavy
rainfall lingers through Saturday.

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

&&

.FIRE WEATHER...
A thermal trough stretches from the southeast Interior to the
central Brooks Range and will stay in place through Friday. This
will allow for isolated thunderstorms to develop east of Fairbanks
and Atigun Pass today and scattered thunderstorms with frequent
lightning developing along the AlCan border. A Red Flag Warning
for lightning remains in effect through midnight tonight for the
area east of Chalkyitsik to Chicken in zones 220 and 224.
Thunderstorms in this area could last all night, with some
producing heavy downpours, gusty winds, frequent lightning, and
small hail. The lowest RH values this afternoon will occur between
Delta Junction and Northway, where they will fall between 18 and
25 percent.

On Thursday thunderstorm coverage will shift west to cover most of
the area east of a line from Umiat to Denali. Scattered
thunderstorms are once again possible along the AlCan border and
shifting further westward and Red Flag conditions for lightning
are possible for the same area as today. Extended the Red Flag
Warnings for zones 220 and 224 through 12 am Friday for this
second round of thunderstorms. Afternoon temperatures will be a
few degrees warmer Thursday than they are today. Minimum RH values
largely remaining above 30 percent

By Friday isolated thunderstorms will occur over most of the Eastern
Interior. An easterly wave moving over the SE Interior Thursday
night into Friday will bring the potential for heavy rain.

&&

.HYDROLOGY...
Between 0.10 to 1.00 inch of rain fell over most of Northern
Alaska west of Atigun Pass to Minchumina in the past 24 hrs,
with the heaviest amounts over south facing slope. Expect rises on
most rivers in the Western Interior, West Coast and Western North
Slope through the weekend. No flooding is expected.

There is the potential for heavy rainfall Thursday night into
Friday across the SE Interior as an easterly wave moves across.
Half an inch to an inch and a half of rainfall accumulation
possible, with the highest amounts falling in the Alaska Range.
This heavy rainfall could cause flooding issues late this week
over the SE Interior.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning for AKZ220-AKZ224.

&&

$$

JUL 21