NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260823_0600
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)
=== ===== === ==== ==== === === === ====
Sun 08/23 06Z 0.10 1514  95  51  11 0.00
Sun 08/23 07Z 0.10 1515  94  62  12 0.00
Sun 08/23 08Z 0.08 1616  93  61  11 0.01
Sun 08/23 09Z 0.06 1616  93  54  11 0.01
Sun 08/23 10Z 0.09 1516  94  42  12 0.01
Sun 08/23 11Z 0.11 1517  94  47  11 0.01
Sun 08/23 12Z 0.09 1619  93  54  12 0.01
Sun 08/23 13Z 0.11 1519  93  59  12 0.01
Sun 08/23 14Z 0.05 1618  94  60  12 0.01
Sun 08/23 15Z 0.05 1718  95  56  12 0.01
Sun 08/23 16Z 0.07 1716  96  71  12 0.01
Sun 08/23 17Z 0.03 1614  95  65  12 0.00
Sun 08/23 18Z 0.03 1713  95  71  12 0.00
Sun 08/23 19Z 0.03 1614  96  77  12 0.00
Sun 08/23 20Z 0.08 1615  96  73  12 0.00
Sun 08/23 21Z 0.10 1616  96  67  13 0.01
Sun 08/23 22Z 0.10 1618  96  60  13 0.01
Sun 08/23 23Z 0.13 1720  98  34  12 0.01
Mon 08/24 00Z 0.38 1921  99  12  12 0.02
Mon 08/24 01Z 0.50 2020  98  19  12 0.02
Mon 08/24 02Z 0.68 2319  95  64  11 0.12
Mon 08/24 03Z 0.52 2417  77  66  12 0.05
Mon 08/24 04Z 0.50 2517  77  61  11 0.00
Mon 08/24 05Z 0.43 2416  75  58  12 0.00
Mon 08/24 06Z 0.37 2415  75  44  12 0.00
Mon 08/24 07Z 0.36 2415  75  42  11 0.00
Mon 08/24 08Z 0.38 2316  73  26  11 0.00
Mon 08/24 09Z 0.40 2317  76  14  11 0.00
Mon 08/24 10Z 0.42 2317  78  20  10 0.00
Mon 08/24 11Z 0.40 2316  75  22  10 0.00
Mon 08/24 12Z 0.33 2314  77  27  10 0.00
Mon 08/24 13Z 0.25 2112  79  33  10 0.00
Mon 08/24 14Z 0.27 2013  83  41   9 0.00
Mon 08/24 15Z 0.31 2014  86  47   9 0.00
Mon 08/24 16Z 0.49 2014  89  63   9 0.00
Mon 08/24 17Z 0.55 2012  90  73   9 0.00
Mon 08/24 18Z 0.91 2012  88  58   9 0.02
Mon 08/24 19Z 1.54 2012  83  44  10 0.02
Mon 08/24 20Z 1.15 2112  87  65  10 0.02
Mon 08/24 21Z 0.54 2215  82  66   9 0.09
Mon 08/24 22Z 0.53 2214  73  47  10 0.01
Mon 08/24 23Z 0.57 2315  75  65  10 0.00
Tue 08/25 00Z 0.57 2314  86  63   9 0.00
Tue 08/25 01Z 0.54 2413  87  71   9 0.00
Tue 08/25 02Z 0.52 2413  84  81   9 0.01
Tue 08/25 03Z 0.54 2413  89  82   9 0.00
Tue 08/25 04Z 0.40 2411  86  90   9 0.01
Tue 08/25 05Z 0.32 2509  89  93   9 0.02
Tue 08/25 06Z 0.31 2609  89  97   9 0.01
Tue 08/25 07Z 0.32 2610  90  98   8 0.01
Tue 08/25 08Z 0.27 2508  91  99   8 0.02
Tue 08/25 09Z 0.26 2508  93  99   8 0.02
Tue 08/25 10Z 0.26 2508  93  99   8 0.01
Tue 08/25 11Z 0.27 2508  93  97   8 0.00
Tue 08/25 12Z 0.30 2609  95  93   8 0.00
Tue 08/25 13Z 0.35 2610  96  89   7 0.01
Tue 08/25 14Z 0.33 2708  96  82   7 0.01
Tue 08/25 15Z 0.33 2708  96  79   7 0.00
Tue 08/25 16Z 0.31 2807  95  78   7 0.00
Tue 08/25 17Z 0.35 2907  95  77   8 0.00

Run total areal avg QPF for the Central_Greens is: 0.62 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