Herndon, PA 17830 Weather

This Hazardous Weather Outlook is for central Pennsylvania.

Day one

Today and tonight.

No hazardous weather is expected at this time.

Days two through seven

Wednesday through Monday.

No hazardous weather is expected at this time.

Spotter information statement

Spotter activation is not expected at this time.

What has changed

* Added mention of fire weather concerns as a key message

Key messages

1) Rain-free and mild conditions will persist through the end of October

2) Trending wetter to start November

3) Fire weather concerns may start to increase later this week.

Discussion

KEY MESSAGE 1: Rain-free and mild conditions will persist through the end of October

Noon Update: Forecast on track. No tweaks worth noting to the next 24 hrs.

Previous discussion: In the wake of a moisture-deprived cold front last night, we'll see another dry day across the Commonwealth with very low dewpoints in northeast PA. Temperatures will be cooler than Monday, but still several degrees above normal for this time of year. The cold front will lift north again as a warm front on Wednesday, bringing increasing clouds but no rain chances.

Temperatures will trend warmer through Friday ahead of another cold front and then decrease a bit into the weekend. Saturday will be similar to Wednesday with increasing clouds but no rain. Daytime and overnight temperatures will be +5 to +15 degrees above average for this time of year through the weekend, providing great conditions for trick or treat. Whether neighborhoods are hosting beggars night on Halloween or moving it earlier, mild and dry conditions will prevail.

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KEY MESSAGE 2: Trending wetter to start November

After not seeing a drop of rain in nearly 2 weeks, November will start off with a couple chances for rain. There remains some model uncertainty, but a trough should move through the central part of the United States early next week. This should deliver enough upper level support to generate some accumulating rainfall across the Commonwealth. Climate Prediction Center outlooks lean wetter than average for the first couple of weeks in November, though the signal is not super strong. Temperature trends favor above normal temperatures with much higher confidence. Notably, the monthly outlook for November begins to take on a classic El Nino pattern with above normal precipitation favored across the southeast US up through the I-95 corridor and below normal precipitation for the Great Lakes. This could set the stage for an active storm track bringing wet conditions to the Lower Susquehanna Valley while the northwest mountains continue their dry trend.

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KEY MESSAGE 3: Fire weather concerns may start to increase later this week.

Min RH values will be lowest this afternoon (mid 30s N to m50s S) and rise for Wed-Thur as dew points increase thanks to return flow as the high pressure overhead moves to the east. The winds will pick up a bit for the same time frame and for Friday, too. The RHs will likely drop some Friday and even further on Sat after a cold front moves through on Friday. This reduction in RH and increase in wind speeds could increase the risk of rapid wildfire spread, especially when combined with any reduction in fuel moisture. Collaboration on Fire Weather issues may be necessary, at the least worthwhile, toward week's end.

Aviation

Thin layer of high level clouds currently moving across central Pennsylvania, generally above 25,000 ft AGL will not bring any threat of sub-VFR conditions in the near-term through 06Z Wednesday. Cloud decks are expected by all model guidance to trend lower at all of central Pennsylvaia's terminals in the 06-12Z Wednesday timeframe as a more expansive cloud deck moves into the region overnight.

Multiple cycles of GLAMP model guidance at AOO/MDT/LNS has led to further thought about adding some mentions of sub-VFR conditions this cycle, with highest confidence in these conditions occurring at AOO. At this time, have pushed AOO towards a prolonged period of MVFR conditions with a shorter period of IFR flight conditions based on a combination of HREF/NBM/GLAMP model guidance. Timing on potential IFR conditions could trend slightly longer compared to current forecast, but increasing winds and slightly less low-level moisture promotes fairly short duration in IFR conditions. Further southeast at MDT/LNS, multiple cycles of GLAMP model guidance outlined LIFR/IFR conditions; however, there is lower (~20-30%) confidence in these conditions occurring as of the 00Z TAF package. Minimum members of HREF ensemble guidance outlines IFR conditions making a fairly close approach to MDT/LNS in the 10-12Z Wednesday timeframe, so this would be the timing of most concern for aviation interests at these two airfields. After 15Z Wednesday, very high confidence in VFR conditions areawide, with another batch of more widespread valley fog potential Wednesday night into Thursday morning.

Outlook:

Thu: VFR likely, AM valley fog possible.

Fri: MVFR ceilings possible mainly in the north and west.

Sat: Mainly VFR conditions.

Sun: Light rain may lead to restrictions, VFR otherwise.

Watches, warnings and advisories

None.