NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260724_0000
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Fri 07/24 00Z 1.28 2812  72  28  10 0.00
Fri 07/24 01Z 1.12 2912  72  24   9 0.00
Fri 07/24 02Z 0.73 2910  72  29   9 0.00
Fri 07/24 03Z 0.55 2909  74  25   9 0.00
Fri 07/24 04Z 0.51 2809  75  17   9 0.00
Fri 07/24 05Z 0.55 2810  72  12   9 0.00
Fri 07/24 06Z 0.52 2809  72  12   9 0.00
Fri 07/24 07Z 0.50 2708  72  15   9 0.00
Fri 07/24 08Z 0.53 2608  72  21   9 0.00
Fri 07/24 09Z 0.51 2508  72  24   9 0.00
Fri 07/24 10Z 0.52 2509  72  27   9 0.00
Fri 07/24 11Z 0.47 2408  73  30   9 0.00
Fri 07/24 12Z 0.48 2409  74  33   9 0.00
Fri 07/24 13Z 0.57 2408  77  33   8 0.00
Fri 07/24 14Z 1.21 2408  79  31   8 0.00
Fri 07/24 15Z 1.83 2408  79  31   9 0.00
Fri 07/24 16Z 2.21 2407  75  33   9 0.00
Fri 07/24 17Z 2.05 2406  71  36  10 0.00
Fri 07/24 18Z 1.88 2505  69  39  10 0.00
Fri 07/24 19Z 1.73 2504  69  41  11 0.00
Fri 07/24 20Z 1.33 2503  69  41  11 0.00
Fri 07/24 21Z 0.90 2603  70  41  11 0.00
Fri 07/24 22Z 0.50 2603  71  42  11 0.00
Fri 07/24 23Z 0.16 2302  71  44  12 0.00
Sat 07/25 00Z 0.15 2303  70  45  12 0.00
Sat 07/25 01Z 0.09 2003  69  43  12 0.00
Sat 07/25 02Z 0.07 1804  68  40  12 0.00
Sat 07/25 03Z 0.08 1906  67  40  12 0.00
Sat 07/25 04Z 0.11 1906  67  40  12 0.00
Sat 07/25 05Z 0.18 2007  68  42  12 0.00
Sat 07/25 06Z 0.22 2107  69  41  12 0.00
Sat 07/25 07Z 0.15 2106  67  38  12 0.00
Sat 07/25 08Z 0.15 2205  65  36  12 0.00
Sat 07/25 09Z 0.13 2403  64  34  12 0.00
Sat 07/25 10Z 0.06 2401  63  32  12 0.00
Sat 07/25 11Z 0.05 1800  63  32  12 0.00
Sat 07/25 12Z 0.07 1402  64  32  11 0.00
Sat 07/25 13Z 0.14 1405  67  32  11 0.00
Sat 07/25 14Z 0.29 1507  70  31  11 0.00
Sat 07/25 15Z 0.58 1607  74  30  11 0.00
Sat 07/25 16Z 0.51 1706  75  29  11 0.00
Sat 07/25 17Z 0.64 1605  75  29  12 0.00
Sat 07/25 18Z 0.90 1505  75  28  12 0.00
Sat 07/25 19Z 1.50 1405  73  25  13 0.00
Sat 07/25 20Z 1.62 1406  74  23  13 0.00
Sat 07/25 21Z 0.85 1506  77  21  13 0.00
Sat 07/25 22Z 0.45 1607  79  22  13 0.00
Sat 07/25 23Z 0.34 1508  81  20  13 0.00
Sun 07/26 00Z 0.24 1610  84  19  12 0.00
Sun 07/26 01Z 0.17 1610  84  18  12 0.00
Sun 07/26 02Z 0.08 1710  84  18  12 0.00
Sun 07/26 03Z 0.06 1808  81  17  12 0.00
Sun 07/26 04Z 0.07 1907  79  16  12 0.00
Sun 07/26 05Z 0.09 2004  80  16  12 0.00
Sun 07/26 06Z 0.10 2103  82  17  12 0.00
Sun 07/26 07Z 0.11 2203  84  17  12 0.00
Sun 07/26 08Z 0.10 2302  87  17  11 0.00
Sun 07/26 09Z 0.10 2602  89  17  11 0.00
Sun 07/26 10Z 0.08 2801  90  18  11 0.00
Sun 07/26 11Z 0.04 0001  89  18  11 0.00

Run total areal avg QPF for the greens is: 0.00 inches.

Froude Number (Frd#): 
Frd# < 0.5 Flow is subcritical and blocked.
         Upslope clouds/precip backed farther upwind of and up to mtn crest.
         W Upslope snow favors eastern Champlain Valley, BTV, and Western slopes.
         Gap winds possible.
Frd# 0.5-1 Flow is subcritical/slow moving/blocked.
         Upslope clouds/precip falls immediately upwind of mtn crest.
         W Upslope snow favors western slopes to the Green Mt. spine including:
         Montgomery,Underhill,Jericho,Bolton,Richmond,Huntington,Lincoln.
         Gap winds possible.
Frd# 1-2 Flow is critical.
         With strong winds, Mountain waves/downslope winds possible.
         Precip falls close to mountain ridge crests and on lee side.
         W Upslope snow favors Green Mt Spine,Jay,Stowe,Waterbury,NE Kingdom.
Froude > 2 Flow is supercritical/unblocked(rapid flow).
         Air flows freely over terrain.
         Persistent upslope snow not favored. Scattered snow showers and flurries.

Relative Humidity (RH): 
         925-850 mb RH > 90% needed for upslope precipitation.
         with 700mb RH > 70% favors upslope snow.
         with 700mb RH > 90% greater amounts of W upslope snow possible.

850mb Temperature (T degC) Westerly Upslope Snow Ratios: (Avg=28:1)
        T > -11       10-15:1
        T -11 to -15  25-35:1
        T < -15       15-20:1