NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260904_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 09/04 18Z 0.63 3209  89  72  12 0.00
Fri 09/04 19Z 0.67 3212  88  77  12 0.03
Fri 09/04 20Z 0.66 3212  86  74  12 0.02
Fri 09/04 21Z 0.47 3212  86  74  12 0.00
Fri 09/04 22Z 0.28 3211  92  84  11 0.01
Fri 09/04 23Z 0.21 3213  90  75  11 0.02
Sat 09/05 00Z 0.20 3314  88  66  11 0.00
Sat 09/05 01Z 0.17 3313  90  73  11 0.00
Sat 09/05 02Z 0.25 3111  94  81  11 0.02
Sat 09/05 03Z 0.26 3214  94  81  10 0.03
Sat 09/05 04Z 0.20 3214  93  76  10 0.01
Sat 09/05 05Z 0.17 3214  93  55  10 0.01
Sat 09/05 06Z 0.15 3314  94  55  10 0.01
Sat 09/05 07Z 0.10 3315  96  60  10 0.02
Sat 09/05 08Z 0.07 3415  97  58  10 0.01
Sat 09/05 09Z 0.05 3515  96  58  10 0.01
Sat 09/05 10Z 0.03 3515  92  54  10 0.01
Sat 09/05 11Z 0.03 3416  91  58  10 0.01
Sat 09/05 12Z 0.04 3516  93  59   9 0.01
Sat 09/05 13Z 0.11 0016  96  62   9 0.01
Sat 09/05 14Z 0.20 0115  96  64   9 0.01
Sat 09/05 15Z 0.24 0113  94  69   9 0.00
Sat 09/05 16Z 0.26 0112  94  70   9 0.00
Sat 09/05 17Z 0.32 0111  94  67   9 0.00
Sat 09/05 18Z 0.29 0111  94  66   9 0.00
Sat 09/05 19Z 0.22 0011  95  64   9 0.00
Sat 09/05 20Z 0.16 0012  95  67   9 0.00
Sat 09/05 21Z 0.18 0014  96  69   9 0.01
Sat 09/05 22Z 0.29 0114  94  70   9 0.00
Sat 09/05 23Z 0.34 0215  96  74   9 0.00
Sun 09/06 00Z 0.45 0317  98  77   8 0.01
Sun 09/06 01Z 0.55 0318  97  78   8 0.01
Sun 09/06 02Z 0.68 0518  95  80   7 0.01
Sun 09/06 03Z 0.77 0516  89  81   7 0.00
Sun 09/06 04Z 0.71 0615  88  74   7 0.00
Sun 09/06 05Z 0.57 0613  86  68   7 0.00
Sun 09/06 06Z 0.42 0512  78  60   7 0.00
Sun 09/06 07Z 0.28 0410  75  57   7 0.00
Sun 09/06 08Z 0.24 0310  72  57   7 0.00
Sun 09/06 09Z 0.25 0212  71  53   7 0.00
Sun 09/06 10Z 0.23 0214  74  53   7 0.00
Sun 09/06 11Z 0.22 0115  76  57   7 0.00
Sun 09/06 12Z 0.17 0115  73  62   7 0.00
Sun 09/06 13Z 0.15 0016  72  62   7 0.00
Sun 09/06 14Z 0.14 0016  74  61   7 0.00
Sun 09/06 15Z 0.11 0015  77  57   7 0.00
Sun 09/06 16Z 0.07 3514  80  53   7 0.00
Sun 09/06 17Z 0.12 3514  81  48   7 0.00
Sun 09/06 18Z 0.23 3513  82  43   7 0.00
Sun 09/06 19Z 0.26 3414  84  31   7 0.00
Sun 09/06 20Z 0.24 3414  85  25   7 0.00
Sun 09/06 21Z 0.16 3414  86  28   7 0.00
Sun 09/06 22Z 0.11 3416  86  32   7 0.00
Sun 09/06 23Z 0.06 3419  84  27   7 0.00
Mon 09/07 00Z 0.06 3520  84  21   7 0.00
Mon 09/07 01Z 0.08 3520  86  39   6 0.00
Mon 09/07 02Z 0.05 3520  84  71   7 0.00
Mon 09/07 03Z 0.04 3418  85  83   7 0.00
Mon 09/07 04Z 0.04 3418  84  81   7 0.00
Mon 09/07 05Z 0.04 3517  86  60   7 0.00

Run total areal avg QPF for the Central_Greens is: 0.29 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