Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261012_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)
=== ===== === ==== ==== === === === ====
Mon 10/12 18Z 0.17 3112  84  59  11 0.00
Mon 10/12 19Z 0.27 3015  83  67  11 0.00
Mon 10/12 20Z 0.38 2918  88  73  10 0.01
Mon 10/12 21Z 0.45 2920  90  67  10 0.01
Mon 10/12 22Z 0.44 3021  92  66   9 0.01
Mon 10/12 23Z 0.41 3124  94  68   9 0.01
Tue 10/13 00Z 0.31 3222  96  63   8 0.01
Tue 10/13 01Z 0.25 3219  97  54   8 0.01
Tue 10/13 02Z 0.18 3216  97  63   7 0.01
Tue 10/13 03Z 0.09 3311  97  71   7 0.00
Tue 10/13 04Z 0.06 3407  97  95   7 0.01
Tue 10/13 05Z 0.07 0203  97  99   7 0.01
Tue 10/13 06Z 0.11 0803  98  99   7 0.05
Tue 10/13 07Z 0.17 1107  98  98   7 0.08
Tue 10/13 08Z 0.16 1311  98  98   7 0.06
Tue 10/13 09Z 0.10 1515  98  98   7 0.09
Tue 10/13 10Z 0.08 1519  97  96   7 0.07
Tue 10/13 11Z 0.06 1620  97  91   7 0.03
Tue 10/13 12Z 0.04 1720  97  98   8 0.02
Tue 10/13 13Z 0.05 1723  97  95   8 0.06
Tue 10/13 14Z 0.05 1725  98  98   8 0.03
Tue 10/13 15Z 0.04 1726  98  97   9 0.08
Tue 10/13 16Z 0.04 1729  98  98   9 0.05
Tue 10/13 17Z 0.05 1731  98  97  10 0.06
Tue 10/13 18Z 0.08 1732  98  88  11 0.09
Tue 10/13 19Z 0.10 1832  98  97  11 0.20
Tue 10/13 20Z 0.16 1831  98  99  12 0.14
Tue 10/13 21Z 0.24 1931  98  99  11 0.20
Tue 10/13 22Z 0.30 2027  98  85  12 0.11
Tue 10/13 23Z 0.36 2128  99  88  12 0.10
Wed 10/14 00Z 0.41 2228  98  90  13 0.14
Wed 10/14 01Z 0.47 2327  98  88  13 0.18
Wed 10/14 02Z 0.51 2327  99  89  13 0.18
Wed 10/14 03Z 0.56 2427  99  79  13 0.08
Wed 10/14 04Z 0.60 2427  99  83  14 0.07
Wed 10/14 05Z 0.72 2428  96  80  13 0.14
Wed 10/14 06Z 0.70 2427  99  79  14 0.09
Wed 10/14 07Z 0.79 2529  98  55  14 0.05
Wed 10/14 08Z 0.91 2530  97  28  13 0.05
Wed 10/14 09Z 1.02 2631  96  10  12 0.03
Wed 10/14 10Z 1.10 2630  95  15  11 0.02
Wed 10/14 11Z 1.17 2731  96  15  10 0.02
Wed 10/14 12Z 1.00 2731  96  28   9 0.02
Wed 10/14 13Z 0.79 2729  94  24  10 0.01
Wed 10/14 14Z 0.69 2729  92  19  10 0.01
Wed 10/14 15Z 0.66 2729  90  40   9 0.01
Wed 10/14 16Z 0.58 2827  88  52  10 0.01
Wed 10/14 17Z 0.62 2826  91  67   9 0.01
Wed 10/14 18Z 0.63 2826  92  64   8 0.02
Wed 10/14 19Z 0.64 2826  94  67   7 0.01
Wed 10/14 20Z 0.62 2826  95  75   6 0.01
Wed 10/14 21Z 0.60 2926  95  71   5 0.01
Wed 10/14 22Z 0.56 2926  96  61   5 0.01
Wed 10/14 23Z 0.53 3027  97  45   4 0.01
Thu 10/15 00Z 0.45 3127  96  26   4 0.01
Thu 10/15 01Z 0.37 3128  96  24   4 0.01
Thu 10/15 02Z 0.36 3229  95  20   3 0.01
Thu 10/15 03Z 0.39 3231  95   6   3 0.00
Thu 10/15 04Z 0.37 3231  95   1   2 0.01
Thu 10/15 05Z 0.39 3231  96   1   2 0.00

Run total areal avg QPF for the Central_Greens is: 2.84 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