NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260501_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)
=== ===== === ==== ==== === === === ====
Fri 05/01 18Z 5.13 2908  66  58   0 0.00
Fri 05/01 19Z 4.99 2808  66  69   0 0.00
Fri 05/01 20Z 3.91 2807  67  73   0 0.00
Fri 05/01 21Z 3.66 2807  68  71   0 0.00
Fri 05/01 22Z 3.07 2706  69  71   0 0.00
Fri 05/01 23Z 0.92 2706  70  70   0 0.00
Sat 05/02 00Z 0.42 2705  68  64   0 0.00
Sat 05/02 01Z 0.29 2704  67  63   0 0.00
Sat 05/02 02Z 0.08 2901  65  67   0 0.00
Sat 05/02 03Z 0.08 1803  65  86   0 0.00
Sat 05/02 04Z 0.11 1704  69  90   0 0.00
Sat 05/02 05Z 0.18 1505  77  93  -1 0.00
Sat 05/02 06Z 0.09 1608  90  98  -1 0.02
Sat 05/02 07Z 0.08 1610  97  98  -1 0.03
Sat 05/02 08Z 0.10 1709  98  93  -1 0.04
Sat 05/02 09Z 0.15 1908  99  84  -1 0.03
Sat 05/02 10Z 0.25 2309  99  82  -1 0.01
Sat 05/02 11Z 0.31 2510  99  79  -1 0.02
Sat 05/02 12Z 0.32 2710  98  72  -2 0.01
Sat 05/02 13Z 0.33 2811  98  79  -2 0.01
Sat 05/02 14Z 0.32 2911  97  75  -2 0.01
Sat 05/02 15Z 0.28 3011  95  72  -2 0.00
Sat 05/02 16Z 0.33 3009  94  69  -3 0.00
Sat 05/02 17Z 0.85 3008  90  59  -3 0.00
Sat 05/02 18Z 1.86 3007  87  39  -2 0.00
Sat 05/02 19Z 2.55 2906  82  24  -2 0.00
Sat 05/02 20Z 2.94 2806  78  26  -1 0.00
Sat 05/02 21Z 1.92 2706  86  47  -1 0.00
Sat 05/02 22Z 0.53 2806  91  50  -1 0.01
Sat 05/02 23Z 0.31 2906  88  43  -1 0.01
Sun 05/03 00Z 0.32 3007  91  46  -2 0.01
Sun 05/03 01Z 0.27 3208  90  43  -2 0.00
Sun 05/03 02Z 0.14 3309  90  42  -2 0.00
Sun 05/03 03Z 0.13 3310  90  39  -3 0.01
Sun 05/03 04Z 0.19 3312  92  35  -3 0.00
Sun 05/03 05Z 0.21 3313  95  33  -3 0.00
Sun 05/03 06Z 0.19 3314  92  33  -3 0.00
Sun 05/03 07Z 0.17 3315  87  36  -4 0.00
Sun 05/03 08Z 0.14 3316  85  37  -4 0.00
Sun 05/03 09Z 0.12 3416  83  38  -4 0.00
Sun 05/03 10Z 0.11 3416  82  41  -4 0.00
Sun 05/03 11Z 0.12 3416  81  46  -5 0.00
Sun 05/03 12Z 0.18 3315  80  48  -5 0.00
Sun 05/03 13Z 1.07 3315  80  44  -5 0.00
Sun 05/03 14Z 2.98 3215  76  38  -4 0.00
Sun 05/03 15Z 4.66 3215  70  40  -4 0.00
Sun 05/03 16Z 5.38 3115  66  45  -4 0.00
Sun 05/03 17Z 6.38 3114  69  50  -3 0.00
Sun 05/03 18Z 6.69 3014  70  56  -3 0.00
Sun 05/03 19Z 6.66 2914  73  52  -3 0.00
Sun 05/03 20Z 6.91 3013  67  57  -2 0.00
Sun 05/03 21Z 6.54 2913  65  50  -2 0.00
Sun 05/03 22Z 5.58 2813  62  48  -1 0.00
Sun 05/03 23Z 3.20 2816  61  46  -1 0.00
Mon 05/04 00Z 1.81 2819  58  39  -1 0.00
Mon 05/04 01Z 1.71 2821  57  36  -1 0.00
Mon 05/04 02Z 1.40 2823  63  16  -1 0.00
Mon 05/04 03Z 1.07 2824  73  91  -1 0.00
Mon 05/04 04Z 1.02 2725  79  86   0 0.00
Mon 05/04 05Z 1.00 2627  83  90   0 0.01

Run total areal avg QPF for the Central_Greens is: 0.23 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