NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260812_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)
=== ===== === ==== ==== === === === ====
Wed 08/12 00Z 0.64 3011  75  67  12 0.00
Wed 08/12 01Z 0.73 3013  75  71  12 0.00
Wed 08/12 02Z 0.74 3115  77  70  12 0.00
Wed 08/12 03Z 0.60 3114  75  68  12 0.00
Wed 08/12 04Z 0.55 3113  74  68  12 0.00
Wed 08/12 05Z 0.53 3113  75  65  12 0.00
Wed 08/12 06Z 0.50 3113  75  63  12 0.00
Wed 08/12 07Z 0.41 3112  75  58  12 0.00
Wed 08/12 08Z 0.35 3111  74  53  11 0.00
Wed 08/12 09Z 0.35 3110  73  55  11 0.00
Wed 08/12 10Z 0.34 3110  71  55  11 0.00
Wed 08/12 11Z 0.34 3009  69  50  11 0.00
Wed 08/12 12Z 0.37 3009  68  51  11 0.00
Wed 08/12 13Z 0.39 3008  68  54  11 0.00
Wed 08/12 14Z 0.58 2808  70  61  11 0.00
Wed 08/12 15Z 1.54 2809  71  61  11 0.00
Wed 08/12 16Z 3.08 2808  70  65  12 0.00
Wed 08/12 17Z 3.81 2807  68  73  12 0.00
Wed 08/12 18Z 3.74 2707  69  84  12 0.00
Wed 08/12 19Z 2.12 2608  72  85  12 0.01
Wed 08/12 20Z 0.80 2610  76  87  12 0.02
Wed 08/12 21Z 0.60 2510  78  83  12 0.01
Wed 08/12 22Z 0.47 2610  77  68  12 0.00
Wed 08/12 23Z 0.41 2608  75  72  12 0.00
Thu 08/13 00Z 0.39 2707  74  79  12 0.00
Thu 08/13 01Z 0.48 2608  78  85  12 0.00
Thu 08/13 02Z 0.53 2510  79  91  12 0.06
Thu 08/13 03Z 0.50 2510  78  92  12 0.01
Thu 08/13 04Z 0.43 2410  78  84  12 0.00
Thu 08/13 05Z 0.41 2410  79  85  12 0.01
Thu 08/13 06Z 0.34 2310  80  89  13 0.01
Thu 08/13 07Z 0.38 2212  83  92  12 0.01
Thu 08/13 08Z 0.30 2212  86  89  12 0.01
Thu 08/13 09Z 0.26 2111  88  90  12 0.01
Thu 08/13 10Z 0.21 2110  87  90  12 0.01
Thu 08/13 11Z 0.19 2108  90  83  12 0.01
Thu 08/13 12Z 0.22 2407  94  74  12 0.01
Thu 08/13 13Z 0.27 2707  96  71  12 0.00
Thu 08/13 14Z 0.34 2810  96  73  12 0.01
Thu 08/13 15Z 0.34 2910  97  72  11 0.01
Thu 08/13 16Z 0.35 3112  98  66  11 0.02
Thu 08/13 17Z 0.32 3213  96  53  11 0.01
Thu 08/13 18Z 0.37 3214  94  45  11 0.00
Thu 08/13 19Z 0.44 3214  92  42  11 0.01
Thu 08/13 20Z 0.47 3217  89  38  12 0.02
Thu 08/13 21Z 0.40 3217  84  39  12 0.03
Thu 08/13 22Z 0.49 3218  81  34  12 0.00
Thu 08/13 23Z 0.90 3121  85  30  11 0.00
Fri 08/14 00Z 0.97 3123  83  34  11 0.00
Fri 08/14 01Z 0.92 3125  82  34  10 0.00
Fri 08/14 02Z 0.99 3225  80  34  10 0.00
Fri 08/14 03Z 0.81 3223  79  34   9 0.00
Fri 08/14 04Z 0.58 3223  78  31   9 0.00
Fri 08/14 05Z 0.49 3322  75  32   9 0.00
Fri 08/14 06Z 0.47 3221  74  34   8 0.00
Fri 08/14 07Z 0.46 3220  74  40   8 0.00
Fri 08/14 08Z 0.47 3220  76  41   8 0.00
Fri 08/14 09Z 0.46 3120  72  43   8 0.00
Fri 08/14 10Z 0.45 3121  70  54   9 0.00
Fri 08/14 11Z 0.43 3121  73  56   9 0.00

Run total areal avg QPF for the 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