NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260824_0000
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)
=== ===== === ==== ==== === === === ====
Mon 08/24 00Z 0.54 2415  89  82  12 0.00
Mon 08/24 01Z 0.59 2416  84  88  12 0.00
Mon 08/24 02Z 0.64 2515  85  77  11 0.00
Mon 08/24 03Z 0.70 2515  85  81  11 0.00
Mon 08/24 04Z 0.58 2615  79  73  11 0.00
Mon 08/24 05Z 0.47 2613  77  76  11 0.00
Mon 08/24 06Z 0.38 2511  73  72  11 0.00
Mon 08/24 07Z 0.39 2312  74  66  10 0.00
Mon 08/24 08Z 0.40 2313  76  67  10 0.00
Mon 08/24 09Z 0.39 2214  80  64  10 0.00
Mon 08/24 10Z 0.41 2215  83  59  10 0.00
Mon 08/24 11Z 0.40 2116  85  62   9 0.00
Mon 08/24 12Z 0.36 2115  86  59   9 0.00
Mon 08/24 13Z 0.40 2116  87  47   9 0.00
Mon 08/24 14Z 0.40 2015  86  45   9 0.00
Mon 08/24 15Z 0.66 2114  84  38   9 0.00
Mon 08/24 16Z 1.74 2113  82  54   9 0.00
Mon 08/24 17Z 3.24 2012  81  61   9 0.00
Mon 08/24 18Z 3.50 1913  80  56  10 0.00
Mon 08/24 19Z 3.25 2115  79  73  10 0.07
Mon 08/24 20Z 0.95 2218  78  49  10 0.02
Mon 08/24 21Z 0.81 2217  73  40  10 0.00
Mon 08/24 22Z 0.74 2215  82  37  10 0.00
Mon 08/24 23Z 0.58 2213  81  48  10 0.00
Tue 08/25 00Z 0.67 2214  85  48  10 0.00
Tue 08/25 01Z 0.82 2315  84  55   9 0.00
Tue 08/25 02Z 0.88 2316  87  64   9 0.00
Tue 08/25 03Z 0.81 2417  91  69   9 0.01
Tue 08/25 04Z 0.68 2416  91  72   9 0.00
Tue 08/25 05Z 0.60 2317  91  84   9 0.00
Tue 08/25 06Z 0.55 2317  91  90   9 0.00
Tue 08/25 07Z 0.52 2416  93  88   9 0.00
Tue 08/25 08Z 0.51 2416  94  79   8 0.00
Tue 08/25 09Z 0.51 2415  96  78   8 0.00
Tue 08/25 10Z 0.51 2415  96  76   8 0.01
Tue 08/25 11Z 0.48 2514  94  74   8 0.00
Tue 08/25 12Z 0.44 2513  95  68   8 0.00
Tue 08/25 13Z 0.47 2514  96  70   8 0.01
Tue 08/25 14Z 0.47 2512  96  75   8 0.00
Tue 08/25 15Z 0.41 2609  97  73   8 0.00
Tue 08/25 16Z 0.36 2707  96  67   8 0.00
Tue 08/25 17Z 0.41 2707  94  63   8 0.00
Tue 08/25 18Z 0.46 2706  95  64   9 0.00
Tue 08/25 19Z 0.48 2708  95  70   9 0.01
Tue 08/25 20Z 0.39 2709  95  86   9 0.03
Tue 08/25 21Z 0.35 2911  93  79   9 0.03
Tue 08/25 22Z 0.35 3012  92  70  10 0.02
Tue 08/25 23Z 0.30 3011  93  62   9 0.01
Wed 08/26 00Z 0.28 3112  94  56   9 0.01
Wed 08/26 01Z 0.27 3112  95  55   9 0.02
Wed 08/26 02Z 0.25 3112  94  50   9 0.01
Wed 08/26 03Z 0.23 3112  94  51   9 0.00
Wed 08/26 04Z 0.22 3112  94  47   9 0.01
Wed 08/26 05Z 0.22 3112  94  42   9 0.01
Wed 08/26 06Z 0.23 3112  92  37   9 0.01
Wed 08/26 07Z 0.22 3112  91  37   9 0.00
Wed 08/26 08Z 0.21 3111  91  35   9 0.00
Wed 08/26 09Z 0.19 3111  91  34   9 0.00
Wed 08/26 10Z 0.17 3211  93  33   9 0.01
Wed 08/26 11Z 0.17 3111  92  31   9 0.00

Run total areal avg QPF for the Central_Greens is: 0.30 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