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KJAN 100654Z 00000KT 6SM BR CLR 22/21 A3020 RMK AO2 SLP223 T02220206= KJAN 100754Z 00000KT 5SM BR FEW085 22/20 A3021 RMK AO2 SLP224 T02170200= KJAN 100854Z 00000KT 5SM BR CLR 21/20 A3020 RMK AO2 SLP222 T02110200 50003= KJAN 100954Z VRB03KT 5SM BR CLR 21/20 A3020 RMK AO2 SLP221 T02110200= KJAN 101054Z 00000KT 4SM BR CLR 21/20 A3022 RMK AO2 SLP228 T02060200= KJAN 101154Z 09003KT 4SM BR CLR 21/20 A3023 RMK AO2 SLP233 T02110200 10228 20206 53008=KJAN 101254Z 08006KT 3SM BR CLR 22/20 A3025 RMK AO2 SLP238 T02220200= KJAN 101354Z 07005KT 4SM HZ CLR 24/21 A3026 RMK AO2 SLP243 T02390206= KJAN 101454Z 08008KT 6SM HZ CLR 27/20 A3026 RMK AO2 SLP243 T02670200 51012= KJAN 101554Z 10007KT 7SM CLR 27/19 A3026 RMK AO2 SLP243 T02720194= KJAN 101654Z 12009KT 9SM CLR 28/18 A3025 RMK AO2 SLP240 T02830183= KJAN 101754Z 06007KT 8SM CLR 29/18 A3024 RMK AO2 SLP235 T02890183 10294 20211 58006= KJAN 101854Z 08007KT 8SM CLR 28/19 A3022 RMK AO2 SLP227 T02830189= KJAN 101954Z 04009KT 8SM CLR 29/19 A3019 RMK AO2 SLP219 T02890189= KJAN 102054Z 07006KT 9SM CLR 29/18 A3018 RMK AO2 SLP214 T02890183 56021= KJAN 102154Z 04007KT 9SM CLR 28/20 A3017 RMK AO2 SLP213 T02780200= KJAN 102354Z 07004KT 10SM CLR 25/19 A3018 RMK AO2 SLP214 T02500189 10294 20250 55002= KJAN 110054Z 08005KT 10SM CLR 24/18 A3018 RMK AO2 SLP216 T02440178= KJAN 110154Z 09007KT 10SM CLR 24/18 A3019 RMK AO2 SLP220 T02390183= KJAN 110254Z 08005KT 10SM CLR 23/18 A3021 RMK AO2 SLP226 T02330178 53013= KJAN 110354Z 09007KT 10SM CLR 23/18 A3021 RMK AO2 SLP224 T02280183= KJAN 110454Z 09006KT 10SM CLR 23/18 A3020 RMK AO2 SLP220 T02280183= KJAN 110554Z 09007KT 10SM CLR 22/18 A3019 RMK AO2 SLP217 T02170178 10250 20217 402940206 58009= KJAN 110654Z 08005KT 9SM CLR 21/18 A3018 RMK AO2 SLP216 T02110178 $= KJAN 110754Z 09005KT 9SM CLR 21/18 A3016 RMK AO2 SLP209 T02110178 $= KJAN 110854Z 10006KT 9SM CLR 21/18 A3015 RMK AO2 SLP204 T02110178 58012 $= KJAN 110954Z 00000KT 9SM CLR 20/18 A3015 RMK AO2 SLP207 T02000178 $= KJAN 111054Z 00000KT 7SM CLR 18/17 A3016 RMK AO2 SLP208 T01830172 $= KJAN 111154Z 00000KT 7SM CLR 18/17 A3017 RMK AO2 SLP212 T01830172 10217 20178 53006 $= KJAN 111254Z 09006KT 7SM CLR 20/18 A3017 RMK AO2 SLP213 T02000178 $= KJAN 111354Z 11008KT 10SM CLR 23/17 A3018 RMK AO2 SLP217 T02330172 $= KJAN 111454Z 11007KT 10SM CLR 27/18 A3019 RMK AO2 SLP217 T02670178 53006 $= KJAN 111554Z 13012KT 10SM CLR 28/17 A3018 RMK AO2 SLP213 T02780167 $= KJAN 111654Z 11012G19KT 10SM CLR 29/16 A3015 RMK AO2 SLP204 T02940161 $= KJAN 111754Z 11012KT 10SM FEW060 30/16 A3012 RMK AO2 SLP193 VIRGA T03000156 10300 20178 58023 $= KJAN 111854Z 11012KT 10SM SCT070 31/14 A3008 RMK AO2 SLP181 T03060144 $= KJAN 111945Z 09009G17KT 10SM SCT075 31/14 A3007 RMK AO2 WSHFT 1927 VIRGA $=I get a low of 69 yesterday morning, followed by a high of 85. Today, a low of 64, followed by a high so far of at least 88.
Why the difference in maxes and mins? Anything obvious? What do you think? I first check the winds: same general winds both days. Then I check the sky conditions: same sky - clear - both days. The biggest difference between yesterday and today seems to be the dew point: it's much lower today than yesterday.
I suspect that's why the minimum temperature was lower today. Remember that the temperature cannot drop below the dew point. Once the dew point is reached, fog and dew may start forming and the dropping temperatures are arrested. Yesterday morning, the dew point was 20.0 C and the minimum temperature was 20.6 C. This morning, the dew point was about 17.2 C and the minimum temperature was 17.8 C. So it seems that both nights the dew point provided a floor for the temperature, so that it could drop no lower.
Based on this, one key forecasting problem for JAN will be deciding what the dew point will be tomorrow morning. To see whether there's drier or moister air coming, I check the current surface map for the southeastern United States. It shows a fairly uniform air mass, with general easterly winds across the entire southeastern United States. The dew points are a bit higher along the Gulf coast, which makes sense: as air passes over the warmer Gulf waters, it picks up moisture. So another thing I'll worry about is whether the wind will change direction slightly and bring more humid air to JAN.
I have a worried thought: what did the surface map look like yesterday? Would I have been able to correctly forecast the drop in dew point which took place? The only map available from yesterday is the 00Z map from yesterday evening, so I pull that up.
I am a bit surprised to find that the air mass was fairly uniform then too. Despite any obvious source of drier air, the whole air mass is gradually becoming drier! That's possible, I guess. I suppose it's been a while since it's rained in the area. As the soil and plants dry out, there's less moisture reaching the atmosphere from the bottom to replace the moisture lost into the atmosphere above.
Okay, maybe that explains why the maximum temperature was warmer today than yesterday. With less heat going into evaporation, more is going into direct heating of the ground and the air above.
There's no reason why that general trend shouldn't continue, so I already have an idea that I'll be forecasting continued warming during the day and cooling at night.
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