NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260718_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)
=== ===== === ==== ==== === === === ====
Sat 07/18 06Z 0.30 2208  59  16  12 0.00
Sat 07/18 07Z 0.47 2311  61  51  12 0.00
Sat 07/18 08Z 0.36 2310  62  89  12 0.00
Sat 07/18 09Z 0.43 2313  61  98  12 0.00
Sat 07/18 10Z 0.49 2315  68  90  11 0.01
Sat 07/18 11Z 0.46 2315  65  96  12 0.00
Sat 07/18 12Z 0.41 2119  70  94  13 0.02
Sat 07/18 13Z 0.47 2122  71  66  14 0.01
Sat 07/18 14Z 0.50 2123  73  59  15 0.00
Sat 07/18 15Z 0.62 2127  81  58  15 0.00
Sat 07/18 16Z 0.75 2127  90  84  15 0.00
Sat 07/18 17Z 0.72 2229  96  78  15 0.41
Sat 07/18 18Z 0.73 2231  93  71  16 0.10
Sat 07/18 19Z 0.84 2231  95  77  16 0.01
Sat 07/18 20Z 0.90 2227  95  77  16 0.02
Sat 07/18 21Z 0.89 2227  94  69  16 0.05
Sat 07/18 22Z 0.89 2227  93  73  16 0.01
Sat 07/18 23Z 0.82 2326  93  79  15 0.01
Sun 07/19 00Z 0.77 2429  95  79  15 0.11
Sun 07/19 01Z 0.78 2528  95  73  15 0.02
Sun 07/19 02Z 0.81 2527  96  62  15 0.03
Sun 07/19 03Z 0.86 2528  95  50  15 0.02
Sun 07/19 04Z 0.90 2629  96  60  14 0.04
Sun 07/19 05Z 0.90 2928  98  63  12 0.05
Sun 07/19 06Z 0.61 3128  94  39  11 0.03
Sun 07/19 07Z 0.40 3229  92  20  10 0.02
Sun 07/19 08Z 0.31 3228  88  17   9 0.01
Sun 07/19 09Z 0.30 3228  86  16   9 0.01
Sun 07/19 10Z 0.30 3229  87  10   8 0.01
Sun 07/19 11Z 0.34 3228  89   6   8 0.01
Sun 07/19 12Z 0.33 3226  89   9   8 0.01
Sun 07/19 13Z 0.32 3224  90   8   7 0.01
Sun 07/19 14Z 0.30 3221  89   4   7 0.00
Sun 07/19 15Z 0.29 3220  85   4   7 0.00
Sun 07/19 16Z 0.38 3218  80   7   7 0.00
Sun 07/19 17Z 2.73 3117  76   8   7 0.00
Sun 07/19 18Z 6.70 3017  71   7   7 0.00
Sun 07/19 19Z 8.47 3017  68  10   8 0.00
Sun 07/19 20Z 8.52 3016  66  11   8 0.00
Sun 07/19 21Z 8.45 3017  63  10   9 0.00
Sun 07/19 22Z 6.62 3018  65   8   9 0.00
Sun 07/19 23Z 3.23 3019  66   7   9 0.00
Mon 07/20 00Z 1.93 3022  64   8   8 0.00
Mon 07/20 01Z 1.53 3123  66   7   8 0.00
Mon 07/20 02Z 1.50 3123  71   7   8 0.00
Mon 07/20 03Z 1.12 3224  73   5   7 0.00
Mon 07/20 04Z 0.72 3224  73   5   7 0.00
Mon 07/20 05Z 0.51 3223  74   5   7 0.00
Mon 07/20 06Z 0.40 3320  75   5   7 0.00
Mon 07/20 07Z 0.31 3318  73   6   7 0.00
Mon 07/20 08Z 0.31 3217  73   7   7 0.00
Mon 07/20 09Z 0.26 3215  74   9   7 0.00
Mon 07/20 10Z 0.22 3213  72  13   8 0.00
Mon 07/20 11Z 0.25 3111  73  22   8 0.00
Mon 07/20 12Z 0.29 3011  73  23   8 0.00
Mon 07/20 13Z 0.33 2909  74  27   8 0.00
Mon 07/20 14Z 0.42 2707  74  35   8 0.00
Mon 07/20 15Z 0.96 2607  74  45   8 0.00
Mon 07/20 16Z 1.64 2507  71  49   8 0.00
Mon 07/20 17Z 1.77 2607  67  58   9 0.00

Run total areal avg QPF for the Central_Greens is: 1.03 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