NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20250322_1800
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sat 03/22 18Z 7.42 2214  59  72   0 0.00
Sat 03/22 19Z 7.67 2115  59  79   0 0.00
Sat 03/22 20Z 9.97 2218  61  94   0 0.00
Sat 03/22 21Z 2.78 2219  78  75   0 0.00
Sat 03/22 22Z 1.54 2320  77  86   0 0.00
Sat 03/22 23Z 1.39 2726  95  90  -1 0.08
Sun 03/23 00Z 1.73 2729  95  82  -3 0.04
Sun 03/23 01Z 1.60 2930  94  36  -6 0.02
Sun 03/23 02Z 1.61 3030  93   3  -9 0.02
Sun 03/23 03Z 3.07 3031  91   2 -12 0.00
Sun 03/23 04Z 3.26 3130  90   9 -13 0.00
Sun 03/23 05Z 3.20 3129  89   5 -14 0.00
Sun 03/23 06Z 2.37 3029  85   4 -15 0.00
Sun 03/23 07Z 1.27 3029  79   4 -15 0.00
Sun 03/23 08Z 0.91 3030  74   5 -16 0.00
Sun 03/23 09Z 0.77 3130  69   6 -16 0.00
Sun 03/23 10Z 0.61 3130  67   6 -16 0.00
Sun 03/23 11Z 0.50 3131  64   7 -15 0.00
Sun 03/23 12Z 0.45 3230  61   7 -15 0.00
Sun 03/23 13Z 0.42 3229  57   8 -15 0.00
Sun 03/23 14Z 0.38 3227  52   8 -14 0.00
Sun 03/23 15Z 0.40 3225  49   9 -14 0.00
Sun 03/23 16Z 0.53 3223  47  10 -14 0.00
Sun 03/23 17Z 0.75 3121  44  11 -14 0.00
Sun 03/23 18Z 0.69 3119  41  11 -13 0.00
Sun 03/23 19Z 0.67 3016  40  11 -12 0.00
Sun 03/23 20Z 0.46 3014  38  11 -11 0.00
Sun 03/23 21Z 0.35 3013  36  10 -10 0.00
Sun 03/23 22Z 0.36 2913  36   9  -9 0.00
Sun 03/23 23Z 0.31 2812  34   8  -8 0.00
Mon 03/24 00Z 0.29 2812  32   9  -7 0.00
Mon 03/24 01Z 0.19 2809  29  13  -5 0.00
Mon 03/24 02Z 0.19 2608  29  14  -5 0.00
Mon 03/24 03Z 0.14 2307  27  17  -4 0.00
Mon 03/24 04Z 0.08 2008  26  19  -3 0.00
Mon 03/24 05Z 0.08 1812  25  20  -3 0.00
Mon 03/24 06Z 0.12 1817  24  15  -3 0.00
Mon 03/24 07Z 0.18 1923  26  27  -3 0.00
Mon 03/24 08Z 0.30 1929  38  90  -4 0.00
Mon 03/24 09Z 0.20 1830  49  98  -4 0.00
Mon 03/24 10Z 0.12 1830  75  97  -2 0.00
Mon 03/24 11Z 0.10 1733  94  97  -1 0.03
Mon 03/24 12Z 0.13 1835  97  97  -1 0.05
Mon 03/24 13Z 0.19 1835  97  86  -1 0.05
Mon 03/24 14Z 0.23 1834  97  61  -2 0.04
Mon 03/24 15Z 0.25 1832  98  33  -2 0.03
Mon 03/24 16Z 0.26 1930  98  10  -2 0.03
Mon 03/24 17Z 0.23 1926  98   5  -1 0.02
Mon 03/24 18Z 0.20 1922  97   6  -1 0.01
Mon 03/24 19Z 0.19 1918  97   5  -1 0.01
Mon 03/24 20Z 0.18 1915  94   9   0 0.01
Mon 03/24 21Z 0.21 2014  87   9   0 0.00
Mon 03/24 22Z 0.21 2113  79  13   0 0.00
Mon 03/24 23Z 0.27 2213  80  38   0 0.00
Tue 03/25 00Z 0.35 2314  92  74  -1 0.01
Tue 03/25 01Z 0.51 2516  97  83  -2 0.06
Tue 03/25 02Z 0.94 2621  96  41  -4 0.02
Tue 03/25 03Z 1.24 2624  94  48  -5 0.01
Tue 03/25 04Z 1.75 2526  91  43  -7 0.01
Tue 03/25 05Z 1.78 2526  87  64  -8 0.00

Run total areal avg QPF for the Central_Greens is: 0.55 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