NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260905_0000
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sat 09/05 00Z 0.32 3214  87  92  11 0.00
Sat 09/05 01Z 0.32 3315  88  88  10 0.00
Sat 09/05 02Z 0.38 3216  90  91  10 0.00
Sat 09/05 03Z 0.38 3217  91  89  10 0.00
Sat 09/05 04Z 0.33 3316  92  84  10 0.00
Sat 09/05 05Z 0.28 3316  92  82  10 0.00
Sat 09/05 06Z 0.21 3315  92  81  10 0.00
Sat 09/05 07Z 0.16 3415  90  81  10 0.00
Sat 09/05 08Z 0.13 3415  90  83  10 0.00
Sat 09/05 09Z 0.11 3515  91  85  10 0.00
Sat 09/05 10Z 0.10 3515  90  83  10 0.00
Sat 09/05 11Z 0.09 3514  90  81  10 0.00
Sat 09/05 12Z 0.08 3514  90  79  10 0.00
Sat 09/05 13Z 0.07 0013  91  77   9 0.00
Sat 09/05 14Z 0.07 0012  92  74   9 0.00
Sat 09/05 15Z 0.12 0111  93  70   9 0.00
Sat 09/05 16Z 0.18 0210  94  69   9 0.00
Sat 09/05 17Z 0.20 0309  95  68   9 0.00
Sat 09/05 18Z 0.18 0208  96  71   9 0.01
Sat 09/05 19Z 0.20 0209  96  75   9 0.02
Sat 09/05 20Z 0.25 0210  96  75   9 0.01
Sat 09/05 21Z 0.28 0311  94  80   9 0.01
Sat 09/05 22Z 0.33 0411  90  85   9 0.02
Sat 09/05 23Z 0.42 0512  80  87   9 0.01
Sun 09/06 00Z 0.43 0513  85  86   9 0.00
Sun 09/06 01Z 0.44 0513  84  87   9 0.00
Sun 09/06 02Z 0.44 0612  83  89   8 0.00
Sun 09/06 03Z 0.45 0712  84  91   8 0.00
Sun 09/06 04Z 0.48 0812  84  93   8 0.00
Sun 09/06 05Z 0.44 0810  83  94   8 0.00
Sun 09/06 06Z 0.33 0908  84  96   7 0.00
Sun 09/06 07Z 0.19 0805  83  96   7 0.00
Sun 09/06 08Z 0.08 0403  83  96   7 0.00
Sun 09/06 09Z 0.05 3504  84  94   7 0.00
Sun 09/06 10Z 0.09 3407  85  91   7 0.00
Sun 09/06 11Z 0.10 3409  86  87   7 0.00
Sun 09/06 12Z 0.07 3512  86  76   6 0.00
Sun 09/06 13Z 0.04 0014  84  62   7 0.00
Sun 09/06 14Z 0.07 0014  82  52   7 0.00
Sun 09/06 15Z 0.11 0012  84  46   7 0.00
Sun 09/06 16Z 0.15 3510  87  45   7 0.00
Sun 09/06 17Z 0.31 3510  89  40   7 0.00
Sun 09/06 18Z 0.46 3411  90  36   7 0.00
Sun 09/06 19Z 0.58 3412  89  30   7 0.00
Sun 09/06 20Z 0.51 3314  88  22   7 0.00
Sun 09/06 21Z 0.35 3316  84  16   7 0.00
Sun 09/06 22Z 0.24 3417  78  16   7 0.00
Sun 09/06 23Z 0.22 3419  77  12   7 0.00
Mon 09/07 00Z 0.20 3420  79  34   7 0.01
Mon 09/07 01Z 0.19 3422  82  40   7 0.01
Mon 09/07 02Z 0.23 3423  87  27   7 0.02
Mon 09/07 03Z 0.15 3522  89  21   7 0.02
Mon 09/07 04Z 0.11 3519  91  27   6 0.01
Mon 09/07 05Z 0.12 3518  91  29   6 0.01
Mon 09/07 06Z 0.11 3518  89  11   6 0.01
Mon 09/07 07Z 0.11 3418  86   6   6 0.00
Mon 09/07 08Z 0.17 3419  86   5   6 0.00
Mon 09/07 09Z 0.21 3419  87   7   6 0.00
Mon 09/07 10Z 0.25 3319  88   8   6 0.00
Mon 09/07 11Z 0.26 3319  88   7   6 0.00

Run total areal avg QPF for the greens is: 0.17 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