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Tracking down Obs deviations at PWM - Portland, ME

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Justin Arnott, modified 9 Months ago.

Tracking down Obs deviations at PWM - Portland, ME

Youngling Posts: 13 Join Date: 9/11/12 Recent Posts

Good Morning,

We're always trying to fine tune temperatures along the coast of Maine where there is such a land/sea temperature difference. However, there has been some interesting behavior lately that I'd like to dig into. Yesterday was a warm day at the coast, but the RTMA/URMA was actually significantly warmer at PWM (Portland Jetport) than observed, which represented the warmest RTMA/URMA temperature anywhere in our CWA. This has occurred on multiple occasions.

I have attached one representative hour in plan view (18Z Sunday), but the table below shows RTMA/URMA/Obs for the daytime yesterday.

PWM Jetport Temps (7/14/2024)
	Obs	RTMA	URMA
8am	73	73	74
9am	77	78	79
10am	81	82	82
11am	83	86	86
12pm	86	89	89
1pm	87	91	92
2pm	86	93	93
3pm	87	92	92
4pm	85	90	90
5pm	83	88	88
6pm	80	85	85
7pm	79	83	83
8pm	78	79	79

Any insight into what is causing temperatures to be so high? Clearly the impact on NBM is less than optimal.

Thanks,
Justin

---

Justin Arnott - Science and Operations Officer

National Weather Service - Gray/Portland, ME

207-688-3221 x224 justin.arnott@noaa.gov

Philippians 1:20

Matthew Morris, modified 9 Months ago.

RE: Tracking down Obs deviations at PWM - Portland, ME

Youngling Posts: 169 Join Date: 12/6/17 Recent Posts

Hi Justin,

Thanks for reaching out. We are taking a look at this and will follow-up with you once we know more.

Matt

On Mon, Jul 15, 2024 at 10:36 AM VLab Notifications <VLab.Notifications@noaa.gov> wrote:

Good Morning,

We're always trying to fine tune temperatures along the coast of Maine where there is such a land/sea temperature difference. However, there has been some interesting behavior lately that I'd like to dig into. Yesterday was a warm day at the coast, but the RTMA/URMA was actually significantly warmer at PWM (Portland Jetport) than observed, which represented the warmest RTMA/URMA temperature anywhere in our CWA. This has occurred on multiple occasions.

I have attached one representative hour in plan view (18Z Sunday), but the table below shows RTMA/URMA/Obs for the daytime yesterday.

PWM Jetport Temps (7/14/2024)

Obs RTMA URMA

8am 73 73 74

9am 77 78 79

10am 81 82 82

11am 83 86 86

12pm 86 89 89

1pm 87 91 92

2pm 86 93 93

3pm 87 92 92

4pm 85 90 90

5pm 83 88 88

6pm 80 85 85

7pm 79 83 83

8pm 78 79 79

Any insight into what is causing temperatures to be so high? Clearly the impact on NBM is less than optimal.

Thanks,
Justin

---
Justin Arnott - Science and Operations Officer
National Weather Service - Gray/Portland, ME

207-688-3221 x224 justin.arnott@noaa.gov

Philippians 1:20

--
Justin Arnott RTMA/URMA Discussion Group Virtual Lab Forum http://vlab.noaa.gov/web/715073/home/-/message_boards/view_message/38657390 VLab.Notifications@noaa.gov

Matthew Morris

SAIC at NOAA/NWS/NCEP/EMC

5830 University Research Ct., Rm. 2038

College Park, MD 20740

301-683-3758

Matthew Morris, modified 9 Months ago.

RE: Tracking down Obs deviations at PWM - Portland, ME

Youngling Posts: 169 Join Date: 12/6/17 Recent Posts

Hi Justin,

Please see the attached slide deck for our findings:

URMA Temperature Case Study - Portland, ME

Slides 2-4 show the background, analysis, observation, and increment figures for the area near KPWM, which is circled on slide 3. The land/sea mask for this area is included on slide 5 (blue pixels are land, white are water).

What we suspect is happening is that two of the nearby land-based observations are being analyzed over water. The positive analysis increment over water spills over land, degrading the analysis near KPWM. One of the observations is from CWOP station E2983 (see slide 6); the innovation (ob minus background) at 20240714/18Z was over 10F. The other observation is from a restricted provider, so I will need to send you a separate message with those details. I can also share the complete KML file, including restricted obs, with you via Kiteworks. Our suggestion is to flag these two stations for temperature on the SDM list to see if it improves URMA temperatures near KPWM. However, doing this would likely reduce the analyzed air temperatures over the ocean.

Note: The grid point nearest KPWM, which you show as 93F in RTMA and URMA, is adjacent to a water grid point, which is much cooler. The background and analysis values in the KML files are derived using bilinear interpolation. For this reason, the URMA analysis value for KPWM is listed as 84.83F in the KML files.

Please let us know if you have any questions and if you'd like to proceed with flagging these two stations.

Thanks,
Matt

On Mon, Jul 15, 2024 at 4:46 PM Matthew Morris - NOAA Affiliate <matthew.t.morris@noaa.gov> wrote: