Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261012_0000
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 00Z 0.11 1819  97  99   7 0.00
Mon 10/12 01Z 0.13 1820  97  99   7 0.07
Mon 10/12 02Z 0.15 1920  98  99   8 0.11
Mon 10/12 03Z 0.17 2014  96  95   9 0.08
Mon 10/12 04Z 0.20 2311  95  94  10 0.03
Mon 10/12 05Z 0.22 2510  94  97  10 0.03
Mon 10/12 06Z 0.21 2710  95  94  10 0.04
Mon 10/12 07Z 0.17 2909  96  91  10 0.02
Mon 10/12 08Z 0.09 3209  97  84  10 0.01
Mon 10/12 09Z 0.06 3311  97  76   9 0.01
Mon 10/12 10Z 0.09 3315  98  64   8 0.01
Mon 10/12 11Z 0.11 3316  98  52   8 0.01
Mon 10/12 12Z 0.09 3314  96  31   9 0.01
Mon 10/12 13Z 0.09 3313  90  27  10 0.00
Mon 10/12 14Z 0.09 3315  85  27  11 0.00
Mon 10/12 15Z 0.09 3316  77  23  12 0.00
Mon 10/12 16Z 0.12 3216  72  21  12 0.00
Mon 10/12 17Z 0.16 3216  70  37  12 0.00
Mon 10/12 18Z 0.22 3116  72  66  12 0.00
Mon 10/12 19Z 0.29 3017  74  68  12 0.00
Mon 10/12 20Z 0.37 2919  83  65  11 0.00
Mon 10/12 21Z 0.41 3020  91  62  11 0.01
Mon 10/12 22Z 0.41 3021  93  68  10 0.01
Mon 10/12 23Z 0.36 3020  95  71  10 0.01
Tue 10/13 00Z 0.32 3119  97  82   9 0.01
Tue 10/13 01Z 0.26 3116  97  84   9 0.01
Tue 10/13 02Z 0.15 3213  97  85   8 0.00
Tue 10/13 03Z 0.10 3311  98  86   8 0.00
Tue 10/13 04Z 0.07 3308  97  93   8 0.00
Tue 10/13 05Z 0.04 3305  97  97   8 0.00
Tue 10/13 06Z 0.02 3201  98  99   8 0.00
Tue 10/13 07Z 0.05 1503  99  96   7 0.01
Tue 10/13 08Z 0.07 1507  99  92   7 0.03
Tue 10/13 09Z 0.05 1612  99  93   7 0.03
Tue 10/13 10Z 0.04 1617  98  88   7 0.04
Tue 10/13 11Z 0.03 1619  98  94   7 0.03
Tue 10/13 12Z 0.03 1622  97  98   8 0.05
Tue 10/13 13Z 0.04 1724  97  93   8 0.05
Tue 10/13 14Z 0.08 1827  98  96   9 0.04
Tue 10/13 15Z 0.11 1828  98  92   9 0.07
Tue 10/13 16Z 0.13 1831  98  91   9 0.06
Tue 10/13 17Z 0.19 1832  98  97   9 0.07
Tue 10/13 18Z 0.24 1931  98  92  11 0.12
Tue 10/13 19Z 0.23 1930  98  95  12 0.16
Tue 10/13 20Z 0.27 2029  97  94  13 0.03
Tue 10/13 21Z 0.31 2030  96  96  13 0.02
Tue 10/13 22Z 0.36 2130  96  89  14 0.01
Tue 10/13 23Z 0.42 2230  96  84  14 0.01
Wed 10/14 00Z 0.49 2331  98  72  14 0.03
Wed 10/14 01Z 0.52 2329  97  74  13 0.04
Wed 10/14 02Z 0.54 2329  99  65  13 0.03
Wed 10/14 03Z 0.59 2429  99  71  13 0.05
Wed 10/14 04Z 0.66 2530  99  67  14 0.07
Wed 10/14 05Z 0.71 2630  98  63  13 0.05
Wed 10/14 06Z 0.71 2627  97  73  13 0.03
Wed 10/14 07Z 0.76 2528  98  80  13 0.04
Wed 10/14 08Z 0.76 2627  98  51  13 0.07
Wed 10/14 09Z 0.80 2626  98  24  12 0.04
Wed 10/14 10Z 0.88 2627  98  16  11 0.04
Wed 10/14 11Z 0.82 2726  97  18  10 0.04

Run total areal avg QPF for the Central_Greens is: 1.84 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