Forecast Verification

Periodically I will take a look at the forecasts made on this page to see how accurate they are. Needless to say, assessing forecasts is very subjective but I will use objective verification whenever possible. Objective results will mainly be taken from the BCC weather station data. When possible, I will make comparisons with other public forecasts for the county made for the same time period.

Forecast from Thursday, Sept. 27: The forecast for Thursday Night was for rain likely developing before daybreak with the probability of precipitation at 60%. The forecast was for less than 0.20 inches of rain. The forecast for rain was accurate. However, the rain arrived slightly earlier than expected, beginning at 3 am, so that 0.24 inches (slightly more than forecast) accumulated by daybreak. The forecast low temperature was mid to upper 40s. The actual low temperature at BCC was 45.4 degrees, which occurred around 11 pm, before the cloud cover moved in. This temperature forecast could also be categorized as accurate.

The forecast for Friday was for: “Overcast, cool and damp, with a steady rain for most of the day. Rain should end in the late afternoon to early evening. Probability of precipitation is near 100%. Rainfall totals should be near 1.00 inch countywide.” It rained most of the day and ended between 6 and 7 pm. Rainfall total for the daytime was 0.97 inches and was near 1.00 inches throughout the county. This forecast was quite accurate. The temperature forecast was for cooler than normal temperatures with a high in the low 50s in the Pittsfield area. The recorded high temperature at BCC was 51.5 degrees. Thus, an accurate temperature forecast.

The forecast for Friday Night: “Remaining mostly cloudy with the chance of a few lingering light showers, mostly before midnight. Probability of precipitation is 40%. Rainfall totals generally less than 0.05 inches.” It remained cloudy overnight with a few light sprinkles totaling 0.02 inches. The forecast was for temperatures remaining steady with a low temperature in the upper 40s. The recorded low temperature at BCC was 50.6 degrees. This is a fairly accurate forecast for a 36 hour period forecast.

Forecast for Saturday: The forecast was for mostly cloudy and cool. This forecast verified objectively although you might disagree with this if you got damp from the drizzle and a few light sprinkles across the county. Still, there was no measurable precipitation (0.00 inches recorded at BCC weather station). This is, however, a fairly accurate forecast for the 48 hour period.

Forecast from Friday, Sept. 27: The forecast for Friday Night was:  “Any scattered light showers in the evening should end by midnight. Remaining overcast. Probability of precipitation 30% early, diminishing after midnight. Any precipitation that falls with evening showers should remain less than 0.05 inches.” Although this forecast was not too bad, there were a few light showers after midnight totaling 0.02 inches. The temperature was forecast to hold steady near 50 degrees and verified at 50.6 degrees.

Saturday: “Overcast and cool. There may be a little spotty drizzle or even a few drips of light rain scattered about the county but  any measurable precipitation is not likely.” Objectively, this is an accurate forecast. Although there was off and on drizzle throughout the day there was no measurable precipitation (0.00 inches at BCC). In fact, a review of multiple weather stations throughout Berkshire County on the Weather Underground website does not indicate any measurable rainfall during the daylight hours. However, it should be noted that one can still get wet from drizzle so this should have been more clearly communicated in the forecast. The forecast high was for upper 50s. The recorded high was 57.9 degrees, an accurate forecast.

Saturday Night: “Remaining mostly cloudy.” This forecast was not accurate from the standpoint the omission of any precipitation as some scattered showers developed before midnight. However, this showers were very widely scattered and although rainfall totaled 0.10 inches at BCC, measurable rainfall was not recorded at most county stations on the Weather Underground site.  A low temperature near 50 was forecast which verified at 52.2 degrees.

Sunday: “Mostly cloudy but breaks in the clouds will likely increase through the day and it may even become partly sunny at times in the afternoon. However, there is the chance of scattered showers developing during the afternoon. Probability of precipitation 40%.”  There was a period of showers in the morning not mentioned in the forecast. The total precipitation before noon was 0.12 inches at BCC. However, this was a small batch of showers only over the westernmost portion of central Berkshire. In fact, it did become partly sunny in the afternoon which destabilized the atmosphere as the low levels warmed and the cool pool associated with the upper-level low moved in aloft. This instability generated a cluster of thunderstorms which moved through the southern and central portions of the county. The forecast high was low 60s, which verified with an actual high of 61.3 degrees. So, to summarize, the overall forecast is fairly accurate for a 48 hour period forecast. The sky cover and temperature forecast were very accurate. The precipitation probability may seem low at 40% but 1) there is greater uncertainty at 48 hours so probabilities are typically lower than will be forecast for a more recent time frame 2) precipitation probability does not mean “40% chance that ANYWHERE in the county will receive rain” it means “40% chance that ANY ONE SPOT will receive rain”. Only about 50-70% of the county received rain so a forecast of 50-70% probability of precipitation for Berkshire County would have been accurate. 3) The 40% probability was higher than the 30% probability forecast on Friday by the NWS and other public forecasts.  Still this forecast would have been improved by the mention of possible thunderstorms, not just showers in the afternoon. There were indications that there would be enough instability to generate thunderstorms in the afternoon and this should have been indicated. Also, there should have been a mention of possible showers in the morning as well as just the afternoon.

To summarize…..objectively speaking, these forecasts were fairly accurate.

I want to mention that although I will make a forecast today there will be no forecasts for the rest of the week due to other obligations.

Summary: Believe it or not, the pesky stationary front and its associated disturbances which have been bringing us occasional rain since Friday still has not cleared the area and its proximity will continue to threaten us with a few scattered showers for the next few days. However, it is finally slowly being pulled north of the county as a warm front as the jet stream shifts to our north (at least temporarily). This will allow temperatures to approach 70 on Wednesday and climb to the unseasonably warm 70s for Thursday and Friday and it will even feel “muggy” as dewpoints reach into the 60s. The front will shift far enough to the north that we will come under the influence of the subtropical high pressure system to our south resulting in considerable sunshine and warm conditions on Thursday and, particularly, on Friday as it will remain sunny but won’t feel quite as muggy as westerly winds bring in some slightly drier air and dewpoints drop back into the 50s. The fair weather will be short-lived, however. A strong cold front will move through the area over the weekend as the jet stream shifts back to the south as a cold trough, presently over western Canada, digs southeast toward the region. Unfortunately, this front will move through very slowly allowing for the threat of showers, particularly Saturday afternoon through Sunday morning. It will turn much cooler as the weekend progresses with temperatures struggling to get out of the 40s on Sunday (hmm…it was just in the 70s on Friday, yikes!!). These types of temperature shifts are typical of this time of year, however, as the sun shifts south of the equator and the meridional (north/south) temperature gradient and the associated jet stream strengthens and shifts south. In any case, hopefully, it will turn sunny and cool early next week as a strong Canadian high pressure system (think autumn) FINALLY moves into the northeast.

Tuesday Night

A few scattered light showers, mainly before midnight. Remaining overcast. Probability of precipitation 50%. Rainfall totals should be 0.10 inches or less.

Overcast skies should keep temperatures from falling. Low temperatures holding steady in the mid to upper 50s.

Light east to southeast winds.

Wednesday

Mostly cloudy in the morning. It may become partly sunny during the afternoon but it will be difficult for the sun to burn away the low clouds with the abundant low level moisture and the lowering sun angle this time of year. In fact, it is possible that it will remain mostly cloudy all day. There is the slight chance of a few scattered light showers. The probability of measurable rainfall is only 20%. However, as on Saturday, there may be some scattered drizzle and sprinkles that could get you wet (or damp at least).

Temperatures will be largely dependent on whether we get any sunshine. Highs will likely be near 70 for most of the county but could reach well into the 70s if we get some afternoon sunshine. It will  begin to feel a little “muggy” in the afternoon as dewpoints climb into the 60s.

Light south to southeasterly winds.

Wednesday Night

Mostly cloudy, humid and unseasonably mild with just the chance of a few scattered light showers and drizzle. Probability of precipitation is 30%. Rainfall totals generally less than 0.05 inches.

Temperatures will fall little with the cloud cover and high humidity with low temperatures in the mid 60s countywide.

Winds will be calm.

Thursday

Becoming partly cloudy, unseasonably warm and humid. There is the slight chance of a residual light shower or sprinkle in the early morning. There is a chance of an afternoon thunderstorm. Probability of precipitation 40%.

High temperatures in the mid 70s for most of the county including Pittsfield and North Adams, with some lower 70s over elevated terrain and in the hilltowns. Highs will likely reach the upper 70s in parts of south county, such as in Great Barrington and Sheffield.

Westerly winds and 5-10 mph.

Thursday Night

Mostly clear. Becoming slightly cooler and less humid as westerly winds winds bring in relatively drier air.

Low temperatures in the low 50s.

Light west to northwesterly winds.

Friday

Mostly sunny and warm.

High temperatures will be similar to Thursday, in the 70s countywide, although it may feel slightly cooler due to lower humidity.

Westerly winds at 10-15 mph.