Update
Update for the long term discussion and 06Z TAF issuance...Front swinging through the panhandle this evening with heavy rainfall rates exceeding a half inch across Ketchikan and Annette Island. Issued a Flood Advisory for Ketchikan area after receiving reports of water over roadways and minor slide activity. Also increased winds from Dixon Entrance to Cape Decision as short term meso models are indicating gale-force winds developing along the frontal passage tonight. The moderate to heavy rain and strong gusty winds will persist through tonight then trend downward through the day Friday. However gusty southerlies will develop benind the front across northern inner channels and Skagway.
Synopsis
Key Messages:
- Moderate to heavy rain continues for much of the panhandle. A flood watch and several flood advisories will persist through Friday afternoon.
- Windy conditions continues through early Friday morning, with high wind warnings and wind advisories for most of the panhandle.
- A strong low moving up Chatham Strait and Lynn Canal will cause quickly changing wind conditions in the inner channels and land areas.
Short Term
Main story tonight into Friday continues to be multiple systems pushing up into the panhandle, rotating around a parent low in the western Gulf, bringing widespread moderate to heavy rain alongside gusty winds to the area. The first round of heavy rainfall will last into the late afternoon to early evening today, currently bringing rain rates of up to 0.15-0.30 in/hr across the panhandle with around 1 to 2 inches already fallen by this afternoon. An additional 1 to 2.5 inches is expected through Friday morning as a second low moves into the panhandle beginning tonight, with the heaviest precipitation still expected across the southern panhandle from Ketchikan up to Petersburg along the coastal range. This low will begin to strengthen and move inland around Chatham Strait / Baranof Island tonight, moving northward over the panhandle and bringing both another burst of elevated winds and a band of heavier precipitation moving up into the central and southern panhandle.
The amounts for the southern panhandle remain largely unchanged through tonight, however the area from Baranof Island up to Juneau is expected to see higher precipitation totals with this increased confidence on the low pushing into the central panhandle. With this additional rainfall, areas from Sitka up along Frederick Sound / Stephens Passage to the Juneau area will see higher rainfall amounts than initially expected, and with it may see some river and creek rises. Juneau in particular may see an additional 1.5 to 2.5 inches through Friday morning, with creeks in Mendenhall Valley now being under a Flood Advisory for minor flooding due to the heavy rainfall. For more information about this, and hydrologic concerns across the rest of the panhandle, see the Hydrology section below.
Long Term
/Saturday through Wednesday/... For the weekend, the active weather pattern will persist at least through Saturday, as lingering low pressure in the northern Gulf will keep onshore flow, mainly cloudy skies and rain showers across much of the Panhandle. As this low weakens, another low passing well to the south will allow a high pressure ridge to build over the Gulf into SEAK. This transition is expected to bring a brief lull in rain showers later Sunday.
The break will be short-lived as another low and front quickly swing through the Gulf into SEAK on Monday, likely reaching Yakutat by the afternoon and then swinging through the panhandle Monday night into early Tuesday. With the quick progression of this system, overall rain amounts will be limited, although a brief period of moderate to heavy rain expected with the frontal passage. Another large, gale force to potential storm force, low will lift northeast into the Gulf of Alaska on Monday night into Tuesday, sending a another front and deep moisture feed toward SEAK. While models agree on the overall general pattern, differences in timing and strength of this low and attendant front still persist. Despite model differences, the low is expected to stall over northern Gulf and weaken by midweek. However, the prolonged onshore flow and a good potential for moderate to heavy rain persists behind the initial front through midweek.
Winds will begin to pick up on Monday night as the front approaches, with breezy to windy southerlies ahead and with the frontal passage Tuesday, with gales possible for Clarence and northern Lynn.
Cooler daytime temps will prevail with the persistent onshore flow, mainly cloudy skies and rain, with highs generally in the mid to upper 40s. Nighttime lows in the upper 30s to low 40s.
Aviation
/Through 6z Saturday/...Widespread MVFR to IFR conditions prevail across the panhandle tonight as a strong front continues to traverse over the area. Some areas are seeing periods of LIFR conditions with CIGs AoB 500 ft as heavier showers move through. However, the majority of sites are staying within low-end IFR with the heaviest rainfall, seeing CIGs around 1500 to 2500 ft and restricted VIS as low as 1 SM. Strong winds are accompanying the lowered conditions, with southeasterly gusts of 20 to 30 kts being seen periodically for many sites. Breaks are expected in between the heavier bands of rainfall, which may bring conditions briefly back up to VFR. Another shortwave band is expected to move into the panhandle within the next few hours, which should bring conditions back down overnight before steadily trending up through the rest of the period. Looks to be potential for more isolated showers and breaks in between around 20z to 0z, with another band moving in for the end of the period. LLWS persists for some areas along the interior and south, but should diminish behind the frontal band.
Marine
Outer waters:
Largely a diminishing trend for the outside waters, with a bulk of the stronger winds over the panhandle. One exception is the western coast of Prince of Wales Island, within the main moisture plume and energy. Therefore, keeping wind speeds around near gale to gale for Dixon Entrance and the western coast of PoW. Similar story for wave heights, with subsiding waves from around 20 ft down to 8-10 ft. Looking to have a convective environment for tomorrow, with a widespread slight chance of thunderstorms in the gulf embedded within the post frontal showers.
Inside Waters:
Complicated forecast for the inner channel waters through Saturday, with a strengthening low pressure system looking to develop and move northward up Chatham Strait and Lynn Canal through Friday morning. East of this system, southeasterlies up to 30 knots will transition sharply to westerlies as the low moves northward. To the northwest of the low as it moves northward, slight westerlies up to 20 knots will persist in places like Icy Strait and Peril Strait. North of the low, light winds to 10 knot northerlies will proceed the low moving over the area. Therefore, expect to see some radically different wind speeds and directions depending on any given locations placement in relation to the low. Behind the low, after the initial westerlies from the cold occluded front, southerly winds will continue well into Saturday.
Hydrology
A strong atmospheric river associated with the current systems moving through will continue to bring heavy rainfall to the panhandle, with continued IVT values of over 500 kg/ms moving into the area. The second wave of this system associated with a low swiftly moving in from the south will still primarily impact the southern panhandle from Ketchikan up to Petersburg. However, the biggest chance in the forecast today is the strengthening of the low as it and moves northward, pushing into the central panhandle tonight and bringing heavier precipitation amounts into the central and northern panhandle. A main band of heavy rainfall looks to impact Baranof Island up to Juneau, bringing an additional 1.5 to 2.5 inches of rain tonight through Friday morning.
With this additional heavier rainfall pushing more northward of the portion of the southern panhandle under a Flood Watch, a Flood Advisory and two Special Weather Statements have been issued. For the Flood Advisory, the heavy rainfall and longer duration for the Juneau area will bring minor flooding to Montana Creek and Jordan Creek by Friday morning, with the Flood Advisory being out until Friday evening due to Jordan Creek in particular taking longer to fall below minor flood stage. For the Special Weather Statements, the rest of Juneau is included in one as other streams in the area besides Montana Creek and Jordan may still see rises into Friday, however flooding is not a concern for these other streams at this time. The other Special Weather Statement is for the central and northern panhandle with the river and creek rises expected with this heavy rainfall, however flooding is also not a concern at this time.
Ajk Watches/Warnings/Advisories
PUBLIC...Wind Advisory from 4 AM to 7 PM AKDT Friday for AKZ318. Flood Watch through Friday afternoon for AKZ326>330-332. Wind Advisory until 10 AM AKDT Friday for AKZ326-329. Wind Advisory until 7 AM AKDT Friday for AKZ327-328. High Wind Warning until 7 AM AKDT Friday for AKZ330-332. MARINE...Gale Warning for PKZ012-036-641-661. Small Craft Advisory for PKZ013-031>035-053-642>644-651-652- 662>664-671-672.
SHORT TERM...Contino LONG TERM...DS AVIATION...ZTK MARINE...NC HYDROLOGY...Contino
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