Tomorrow (12Z April 12th - 0Z April 13th): A blend of sun and clouds during the day with some increasing clouds in the later afternoon. Northerly wind at 10mph. High 59°. 20% chance of showers after 4pm with precipitation accumulations of less then a tenth of an inch.
Tomorrow Night (0Z April 13th - 12Z April 13th): 10mph Northeasterly winds calming to about 5mph throughout the evening. Mostly cloudy skies with a 40% chance of showers after 2am. Low 39°.
Wednesday (12Z April 13th - 0Z April 14th): Cloudy most of the day with a few possible breaks of sun after 2pm. High temperature of 46°. East wind 5-10mph with slightly gustier periods throughout the day. Showers likely, a 70% chance of precipitation accumulation of up to a tenth of an inch possible.
Initial Conditions (that lead to public forecast)
Starting with the initial conditions of April 11th visibly seen on satellite images, there was a high pressure system located over the interior portions of the United States. This made conditions relatively quiet for most of the central U.S. However, in our Northeast area, there was a low pressure system moving eastward off of the Gulf of Maine. When viewing the IR satellite, looking back in time (12 hours), you could see the higher and colder cloud tops located around the areas of Plymouth which corresponded to the timing that we experienced a few thunderstorms earlier that morning. The water vapor image portrayed a nice, cyclonic circulation over Quebec. The other more evident feature was the moisture moving out of our area throughout the day along with the low pressure system (I knew that this would play an important part in my forecast). The radar imagery across the US displayed the precipitation that we were experiencing on this day tapering off and becoming very "jagged" (feature-wise) as the day moved on.
In terms of the initial conditions of the upper atmosphere. At 250mb, there was a fairly large trough that began positively tilted on April 10th. A strong jet over the middle portions of the U.S. caused the trough to neutralize in its orientation. Finally, the trough lifted-out around the time of my forecast period. For 500mb, I started looking at the night of April 10th. When looking towards the Gulf it was extremely evident that there was warm, moist air feeding off of the Gulf to drive the storms that were seen in Iowa / around the Midwest that day. The 850mb analysis reiterated the warm air advection from the Gulf . The 850 low pressure portrayed a nice height gradient, which really supplied the moisture off of the gulf to push some warm air advection even as high as New England into the morning of my forecast period which is why we experienced a few thunderstorms.
Starting the forecast....
Around 10:30 the morning of April 11th, there were thunderstorms moving through the area. However, the storms cleared out pretty quickly and there was some cloud clearing by noon with lots of evaporation taking place within Plymouth as a result. This would have been a big player on the days high temperature, however the clouds (although they cleared slightly), continued to linger around Plymouth, so we were only able to obtain a high in the mid 50's.
When making the overnight forecast for the 11th, I was looking toward the GFS. I saw some heavier precipitation on the 6hr left over around 6Z. I decided to forecast for a slight chance of rain overnight. With the low pressure system continuing to pass over the Plymouth area that night, I noticed a wind shift, so I accounted for the Northwesterly winds blowing at a steady 10mph. In terms of the overnight low the forecast Skew-T that I was looking at from the NAM, did not show a temperature drop until right before 12Z. I decided to take that value and use the mix out method and refer to MOS in order to come up with a slightly warm overnight low of 47°.
For Tuesday's forecast, when I started to account for the high temperature for the day after using the mix out method, I came up with a high of 59°. I decided to keep this temperature although 700mb relative humidity was aiming towards a cloudier day, I did not reduce the temperature for clouds because I noticed that Plymouth was going to "dry-up" in terms of the relative humidity just around the time where Plymouth experiences its warmest part of the day. When checking MOS and 6-hr precipitation, I noticed that both MOS and the GFS itself had a trace of some precipitation occurring within the later afternoon hours. I decided to call for a 10% slight chance of precipitation. In terms of the winds, due to another low pressure system moving to the south of Plymouth, I also accounted for another wind shift of NE from NW during that Tuesday.
Tuesday night's forecast was definitely a tricky one especially in terms of the overnight low temperature. I had forecasted for clouds all night with a possibility of some cooling due to a chance of precipitation (40%). However, the 850mb temperatures were fairly warm overnight. I continued to keep what I had in mind for the winds, precipitation, clouds, etc. And after using the mix out method due to all of this, I checked with MOS and found a sort of an average of 39° for the overnight low to play it safe.
For Wednesday, I first looked at the 700mb relative humidity. I saw a break in the humidity around 18Z however, due to the rest of the conditions I considered while forecasting, I did not exactly make this break in the clouds a large player in my forecast. 6hr. precipitation was showing a decent amount of precipitation and when I was looking at the vorticity, I saw that the vorticity maximum was increasing and reaching our area throughout the day. Also, looking at the 850mb analysis, the 850 Low looked like it was going to linger around the area, which gave me even more of an incentive to give a 90% chance of showers on Wednesday. My high temperature of 46° consisted of using the mix out method and taking off 10° for clouds and the likely chance of showers.
Forecast Verification
For the April 11th-12th overnight low, I forecasted 47° with a POP of 30. The actual was 46° and there was a trace of precipitation (100%).
On Tuesday April 12th I forecasted the high temperature of 59° with a POP of 10. The actual was dead on at 59° however there was no trace of precipitation.
Tuesday night, my forecast was a low temperature of 39° with a POP of 40. The actual was 38°, precipitation was zero, but a trace was recorded.
Wednesday, I forecasted for a high of 46° with a POP of 90. Once again, I was right on with the high of 46° and there was precipitation recorded for that day (100%).
When I had verified my forecast, I was pleased with my forecasted temperatures because if they were not dead on, they were within the ballpark of the actual recorded temperatures. I do take a lot into consideration when forecasting for low and high temperatures. I like using the mix out method and then modifying it because I can look at what I mix out to be, and then consider what else is going on for that period. Cloud cover, winds, any precipitation, etc. are all areas that I look at when I "tweak" my temperature forecasts. The other thing that I had worked on since my last forecast journal was taking MOS into consideration instead of just what the National Weather Service was calling for. Looking back on my first journal, I had mentioned that MOS was definitely something I should start taking a look at. I am glad to say that I worked on doing this because MOS really helped me out for this forecast period.
For areas of improvement, I want to this time consider precipitation forecasting. I think that I had relied too heavily on the GFS, especially in terms of forecasting for precipitation. If I saw 6hr. precipitation shading even on the boarder of Plymouth, I felt like I had to forecast for at least a POP of 10. I have also noticed that 6hr. precipitation is really the only factor I look into when forecasting for precipitation. After viewing many of the weather discussions this semester, I realize that I need to start considering variables such as: When a front is going to be passing over our area and what time, upper level dynamics, soundings (with something as simple as if they are dry or not), ensembles, etc. This is something that I have been working on since this forecast period and will continue to do so to enhance my forecasting skills from here on out.
