NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260823_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)
=== ===== === ==== ==== === === === ====
Sun 08/23 00Z 0.37 1415  90  52  11 0.00
Sun 08/23 01Z 0.37 1417  89  41  11 0.00
Sun 08/23 02Z 0.29 1417  87  31  12 0.00
Sun 08/23 03Z 0.23 1417  83  25  12 0.00
Sun 08/23 04Z 0.17 1517  82  28  12 0.00
Sun 08/23 05Z 0.14 1617  84  33  12 0.00
Sun 08/23 06Z 0.15 1618  86  40  12 0.01
Sun 08/23 07Z 0.16 1620  88  48  11 0.01
Sun 08/23 08Z 0.13 1620  91  54  11 0.01
Sun 08/23 09Z 0.13 1619  92  55  11 0.01
Sun 08/23 10Z 0.14 1618  93  55  11 0.01
Sun 08/23 11Z 0.12 1617  92  56  11 0.01
Sun 08/23 12Z 0.12 1617  91  59  11 0.01
Sun 08/23 13Z 0.12 1616  90  62  12 0.01
Sun 08/23 14Z 0.11 1616  90  65  12 0.00
Sun 08/23 15Z 0.13 1616  91  66  12 0.00
Sun 08/23 16Z 0.13 1616  93  74  12 0.00
Sun 08/23 17Z 0.08 1714  94  74  12 0.00
Sun 08/23 18Z 0.08 1713  95  74  12 0.00
Sun 08/23 19Z 0.12 1613  95  72  13 0.00
Sun 08/23 20Z 0.11 1714  94  73  13 0.00
Sun 08/23 21Z 0.17 1616  94  67  13 0.00
Sun 08/23 22Z 0.17 1618  94  64  13 0.01
Sun 08/23 23Z 0.08 1721  94  76  13 0.01
Mon 08/24 00Z 0.05 1823  94  59  13 0.01
Mon 08/24 01Z 0.17 1924  94  43  13 0.01
Mon 08/24 02Z 0.44 2220  90  79  12 0.17
Mon 08/24 03Z 0.52 2318  83  48  12 0.07
Mon 08/24 04Z 0.44 2416  84  40  11 0.00
Mon 08/24 05Z 0.44 2416  84  35  11 0.00
Mon 08/24 06Z 0.37 2414  85  31  11 0.00
Mon 08/24 07Z 0.35 2414  86  40  11 0.00
Mon 08/24 08Z 0.31 2312  87  38  11 0.00
Mon 08/24 09Z 0.26 2311  85  42  11 0.00
Mon 08/24 10Z 0.26 2311  85  44  10 0.00
Mon 08/24 11Z 0.24 2311  85  45  10 0.00
Mon 08/24 12Z 0.20 2210  84  48  10 0.00
Mon 08/24 13Z 0.19 2209  86  53  10 0.00
Mon 08/24 14Z 0.14 2108  87  53   9 0.00
Mon 08/24 15Z 0.12 2008  88  53   9 0.00
Mon 08/24 16Z 0.26 2109  90  58   9 0.00
Mon 08/24 17Z 0.45 2109  90  66   9 0.00
Mon 08/24 18Z 0.65 2110  86  64   9 0.00
Mon 08/24 19Z 1.10 2210  83  63   9 0.03
Mon 08/24 20Z 1.59 2211  81  55   9 0.01
Mon 08/24 21Z 1.09 2211  82  59   9 0.00
Mon 08/24 22Z 0.68 2312  85  50   9 0.00
Mon 08/24 23Z 0.50 2413  83  41   9 0.02
Tue 08/25 00Z 0.54 2413  80  31   9 0.02
Tue 08/25 01Z 0.58 2514  80  33   9 0.00
Tue 08/25 02Z 0.61 2614  84  33   9 0.00
Tue 08/25 03Z 0.55 2613  85  44   8 0.00
Tue 08/25 04Z 0.53 2613  84  45   8 0.00
Tue 08/25 05Z 0.49 2513  82  44   8 0.00
Tue 08/25 06Z 0.42 2512  82  51   8 0.00
Tue 08/25 07Z 0.38 2511  83  60   8 0.00
Tue 08/25 08Z 0.33 2510  82  62   8 0.00
Tue 08/25 09Z 0.29 2410  84  66   8 0.00
Tue 08/25 10Z 0.30 2411  88  76   8 0.00
Tue 08/25 11Z 0.31 2411  89  83   8 0.00

Run total areal avg QPF for the greens is: 0.44 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