NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260509_0600
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)
=== ===== === ==== ==== === === === ====
Sat 05/09 06Z 0.60 2512  60  49   0 0.00
Sat 05/09 07Z 0.76 2512  58  44   0 0.00
Sat 05/09 08Z 0.62 2511  55  42   0 0.00
Sat 05/09 09Z 0.49 2509  50  38   0 0.00
Sat 05/09 10Z 0.45 2309  50  41   0 0.00
Sat 05/09 11Z 0.34 2110  52  42   0 0.00
Sat 05/09 12Z 0.27 1912  57  41   0 0.00
Sat 05/09 13Z 0.24 1812  64  41   0 0.00
Sat 05/09 14Z 0.53 1712  68  49   0 0.00
Sat 05/09 15Z 1.08 1613  73  60   1 0.00
Sat 05/09 16Z 1.26 1615  78  67   1 0.00
Sat 05/09 17Z 1.02 1617  84  72   1 0.01
Sat 05/09 18Z 0.87 1619  88  74   1 0.03
Sat 05/09 19Z 0.96 1620  91  74   1 0.03
Sat 05/09 20Z 0.22 1620  94  73   1 0.03
Sat 05/09 21Z 0.08 1719  96  73   2 0.01
Sat 05/09 22Z 0.08 1718  95  78   3 0.01
Sat 05/09 23Z 0.09 1818  95  76   3 0.01
Sun 05/10 00Z 0.10 1820  95  63   3 0.01
Sun 05/10 01Z 0.20 1922  97  53   3 0.01
Sun 05/10 02Z 0.27 2024  96  30   3 0.01
Sun 05/10 03Z 0.30 2025  95  20   4 0.01
Sun 05/10 04Z 0.41 2126  93  22   4 0.01
Sun 05/10 05Z 0.34 2026  86  21   5 0.01
Sun 05/10 06Z 0.35 2127  81  35   6 0.01
Sun 05/10 07Z 0.50 2130  84  66   6 0.01
Sun 05/10 08Z 0.58 2229  85  85   6 0.00
Sun 05/10 09Z 0.64 2328  91  93   5 0.01
Sun 05/10 10Z 0.74 2427  95  83   4 0.03
Sun 05/10 11Z 0.85 2524  94  67   3 0.03
Sun 05/10 12Z 0.88 2622  93  69   2 0.01
Sun 05/10 13Z 1.06 2621  86  60   1 0.02
Sun 05/10 14Z 2.44 2519  79  39   1 0.02
Sun 05/10 15Z 5.75 2518  78  11   1 0.00
Sun 05/10 16Z 7.68 2517  72  12   1 0.00
Sun 05/10 17Z 11.24 2517  59  16   1 0.00
Sun 05/10 18Z 11.78 2516  50  20   2 0.00
Sun 05/10 19Z 11.77 2616  45  21   2 0.00
Sun 05/10 20Z 11.63 2616  45  22   2 0.00
Sun 05/10 21Z 11.28 2616  48  23   2 0.00
Sun 05/10 22Z 9.33 2716  53  21   1 0.00
Sun 05/10 23Z 5.68 2718  57  22   1 0.00
Mon 05/11 00Z 2.13 2721  59  20   0 0.00
Mon 05/11 01Z 1.61 2821  58  21   0 0.00
Mon 05/11 02Z 1.55 2823  60  22  -1 0.00
Mon 05/11 03Z 1.24 2821  70  20  -2 0.00
Mon 05/11 04Z 1.02 2921  78  22  -2 0.00
Mon 05/11 05Z 0.93 2921  78  23  -3 0.00
Mon 05/11 06Z 0.84 2919  80  22  -3 0.00
Mon 05/11 07Z 0.72 3018  76  21  -3 0.00
Mon 05/11 08Z 0.67 3017  75  21  -3 0.00
Mon 05/11 09Z 0.62 2916  75  21  -3 0.00
Mon 05/11 10Z 0.62 2915  74  21  -3 0.00
Mon 05/11 11Z 0.65 2915  74  21  -4 0.00
Mon 05/11 12Z 0.75 2815  72  22  -4 0.00
Mon 05/11 13Z 2.27 2814  70  21  -4 0.00
Mon 05/11 14Z 5.84 2812  71  25  -4 0.00
Mon 05/11 15Z 6.84 2811  70  26  -3 0.00
Mon 05/11 16Z 6.96 2811  66  26  -3 0.00
Mon 05/11 17Z 6.44 2810  65  26  -2 0.00

Run total areal avg QPF for the greens is: 0.33 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